Chiral host-guest catalysis : enantioselective epoxidation of unfunctionalized alkenes

Li, Zengmin (1999) Chiral host-guest catalysis : enantioselective epoxidation of unfunctionalized alkenes. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[img] [English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version
Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.

Download (27Mb)
  • [img] [English] PDF - Accepted Version
    Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.
    (Original Version)

Abstract

Catalytic asymmetric synthesis is the most effective and challenging approach to obtain enantiomerically enriched organic compounds. This research focused 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 (1R.2R)- or (1S.2S)-cyclohexane-1.2- 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 CDCl₃ 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.

Item Type: Thesis (Doctoral (PhD))
URI: http://research.library.mun.ca/id/eprint/863
Item ID: 863
Additional Information: Includes bibliographical references
Department(s): Science, Faculty of > Chemistry
Date: 1999
Date Type: Submission
Library of Congress Subject Heading: Chirality; Enantiomers; Catalysis; Asymmetric synthesis

Actions (login required)

View Item View Item

Downloads

Downloads per month over the past year

View more statistics