| Summary: | Thesis (Ph.D.)--Memorial University of Newfoundland, 1999. Chemistry Includes bibliographical references Catalytic asymmetric synthesis is the most effective and challenging approach to obtain enantiomerically enriched organic compounds. This research focussed on development of new chiral salen-based macrocyclic catalysts for catalytic asymmetric synthesis, particularly asymmetric epoxidation of unfunctionalized alkenes. -- Template-directed reactions of dialdehydes and (IR.2R)- or (1S.2S) cyclohexane -1.1- diamine gave three series of macrocyclic salen dimers. A single-crystal X-ray study of the first series. 26-membered macrocycles having -CH2- links, showed a novel calixarene- like structure with a 1.3-alternate conformation in the solid state. NMR studies revealed that a single conformer was maintained in solution for this series of macrocycles. However, the related 32-membered macrocyclic salen dimer containing longer -(OCH2)2- links was flexible and showed four conformers in CDC13 at room temperature. -- Sequentially, controlled complexation of the macrocyclic salen dimers afforded mononuclear (C1 symmetric) and binuclear (C2 symmetric) complexes. Host/guest interactions of the mononuclear complexes were demonstrated through 1H NMR titration experiments. For the binuclear complexes, two cofacial salen units adopted a syn- or anti- conformation with respect to the cyclohexyl rings relative to a cavity defined by four benzene units. An intramolecular inclusion compound between a binuclear Ni(II) macrocyclic complex and a non-aromatic guest, acetonitrile. was structurally determined by X-ray diffraction. -- Electrocatalytic studies using the rotating ring-disk technique showed that the activity and selectivity of a binuclear calixsalen cobalt complex compared favourably with that of a face-to-face porphyrin catalyst reported by Collman for catalytic reduction of dioxygen at biological pH. -- Catalytic epoxidation studies showed that binuclear Mn(III) complexes had moderate enantioselectivity. An ee of 72% was achieved in the epoxidation of styrene at ambient temperature. The new binuclear catalysts were size-selective and both X-ray and MMX modelling studies of a model complex supported the experimental observations. This research provided the first strong experimental evidence for host/guest catalysis in asymmetric epoxidation.
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