title: Structure, modelling and dynamic behaviour of aza- and azaoxamacrocyclic ligands derived from (R,R)-1,2-diaminocyclohexane.
abstract: Investigations into the conformational behaviour of macrocyclic ligands 5 and 6 derived from (R,R)-1,2-diaminocyclohexane have been undertaken using molecular modelling, single crystal X-ray diffraction and variable temperature 1H NMR spectroscopy. These have revealed that the lowest energy conformers in both cases do not possess the expected C2-element of symmetry, which can only be accessed at higher temperatures. Instead both molecules exist as C1-conformers at room temperature and in the solid state. In solution a range of dynamic exchange processes is observed which result, in part from the inherent strain in these fused bicyclic systems. An unexpected but characteristic feature of the C1-symmetric conformers is highlighted by the presence of a signal at unexpectedly low field in their 1H NMR spectra due to the interaction of two of the sulfonyl oxygen atoms with one of the bridgehead hydrogen atoms.
authors.affiliation: Department of Chemistry, Queen Mary, University of London, Mile End Road, London, UK E1 4NS.
authors.forename: Sonia
authors.initials: S
authors.lastname: Pulacchini
authors.forename: Rima
authors.initials: R
authors.lastname: Nasser
authors.forename: Kevin F
authors.initials: KF
authors.lastname: Sibbons
authors.forename: Majid
authors.initials: M
authors.lastname: Motevalli
authors.forename: Geoffrey E
authors.initials: GE
authors.lastname: Hawkes
authors.forename: Romano T
authors.initials: RT
authors.lastname: Kroemer
authors.forename: Edson S
authors.initials: ES
authors.lastname: Bento
authors.forename: Michael
authors.initials: M
authors.lastname: Watkinson