A series of conjugated [3+3] Schiff-base macrocycles containing both a central
crown ether-like pocket and three tetradentate N[sub 2]O[sub 2] binding sites were prepared and
investigated. The formation mechanism was investigated through the synthesis and study
of macrocycle fragments. Further understanding of the macrocycle conformations and
dynamics was obtained through computational studies.
A monoreduced macrocycle where one of the six imines has been reduced was
obtained as a by-product of macrocycle formation. Reactivity studies and deuterium
labeling investigations revealed that the selective reducing agent is likely a
benzimidazoline. This intermediate is generated in situ during the formation of the nonreduced
macrocycle and with macrocycle reduction is converted to a stable
benzimidazole unit.
Upon addition of small cations, the conjugated Schiff-base macrocycles assemble
into tubular structures. Spectroscopic and mass spectrometric studies have shown that the
cations bind to the crown ether-like centre of the macrocycle and induce aggregation to
form structures composed of alternating cations and macrocycles.
With the addition of seven equivalents of Zn[sup 2+] or Cd[sup 2+] to these fully conjugated
macrocycles surprising heptametallic complexes were obtained. Here, the trimetallated
macrocycle is first formed (with metal ions bound to the three N[sub 2]O[sub 2] pockets) and then
this templates the formation of a [M[sub 4]O][sub 6+] cluster that caps the cone-shaped macrocycle.
NMR studies indicated that these zinc complexes dimerize under certain solvent conditions forming capsule-like structures resembling cavitands used in host-guest
chemistry.
Variations of these [3+3] Schiff-base macrocycles were prepared by modifying
the substituents of the diformyl diol unit. In this way naphthalene-based macrocycles
were prepared. Studies on a series of related model compounds revealed that the ketoenamine
isomer is stabilized in these macrocycles rather than the enolimine isomer as
observed in the analogous phenyl-based macrocycles.Science, Faculty ofChemistry, Department ofGraduat