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Memorial University - Electronic Theses and Dissertations 3
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TitleTransition metal-mediated diastereoselective synthesis of metallophosphinates
AuthorZhou, Zhongxin, 1962-
DescriptionThesis (Ph.D.)--Memorial University of Newfoundland, 1994. Chemistry
Date1994
Pagination421 leaves : ill.
SubjectChirality; Asymmetric synthesis; Enantiomers; Transition metals
DegreePh.D.
Degree GrantorMemorial University of Newfoundland. Dept. of Chemistry
DisciplineChemistry
Languageeng
NotesBibliography: leaves 256-377
AbstractNew methods and tools have led to optimized ship structure, but poorly designed details persist, leading to fatigue failure. The cost of optimizing all details is prohibitive. Transition metal-mediated diastereoselective synthesis is one of the most important and extensively used methods to create chiraiity at carbon and other heteroatom centres. This thesis focuses on chiral induction from an asymmetric, pseudo-octahedral metal centre in the Arbuzov-like dealkylation of prochiral phosphonites. A series of if-cyclopentadienyl, η5-pentamethylcyclopentadienyl, and η5-indenyl three- legged piano-stool complexes have been studied as chiral auxiliaries. The effects of ligand sphere steric and electronic properties on M* P optical induction have been examined. -- The synthesis, structure, spectroscopic properties of a series of chiral rf-indenyl cobalt complexes are described. X-ray crystal structure and solution conformational analysis showed that all η5-indenyl complexes have a propensity to distort away from η5 toward if coordination, and that the indenyl ring always has certain conformational preferences with respect to the ligands on the metal. Distortion and conformational preferences of indenyl complexes are fully discussed on the basis of extended Huckel molecular orbital (EHMO) calculations, and fragment molecular orbital (FMO) analysis. -- Arbuzov reactions of η5-indenyl, η5-cyclopentadienyl, and η5-pentamethyIcyclopenta-dienyl cobalt iodide auxiliaries with PR'(OMe)2 (R' = OMe, Ph) proceed via an ionic mechanism to form the corresponding cobaltophosphonates or phosphinates. Ionicintermediates were observed by 1H NMR spectroscopy at ambient temperature in most cases and isolated in some cases. -- The following conclusions can be drawn from the results presented in this thesis: (i) The chiral metal center is essential for stereoselectivity, (ii) The steric requirements of the spectator ligands is crucial in determining chiral induction. The bulkier the spectator ligands, the higher the chiral induction. (iii) The stereochemical properties of the entering phosphonites, PR'(OMe)2 is also important for diastereoselectivity. Large substituent R' result in high diastereoselectivity. (iv) Intramolecular hydrogen bonding plays a significant role in controlling the stereoselectivity in the Arbuzov reaction by restricting population of solution conformations, maximizing the preference of one diastereomer over another.
TypeText
Resource TypeElectronic thesis or dissertation
FormatImage/jpeg; Application/pdf
SourcePaper copy kept in the Centre for Newfoundland Studies, Memorial University Libraries
Local Identifier76221203
RightsThe 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.
CollectionElectronic Theses and Dissertations
Scanning StatusCompleted
PDF File(44.62 MB) -- http://collections.mun.ca/PDFs/theses/Zhou_Zhongxin.pdf
CONTENTdm file name190395.cpd