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Title: Syntheses, structures and reactivities of metallated organophosphane oxides
Author: Dunbar, L.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1999
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This thesis describes the syntheses and characterisations of lithiated alkyldiphenylphosphane oxides, used in the long-established Horner-Wittig reaction whereby aldehydes and ketones are converted to alkenes. In addition, nitrile insertion reactions of these species, leading to the formation of novel enamides (with N...C...C azaallyl functions), have been investigated. Chapter 3 deals exclusively with Horner-Wittig chemistry. It reports the first crystalline unsolvated lithiated phosphane oxides [Ph2P(O)CH(Li)CH(Me)Et]4.C6H5CH3 and [Ph2P(O)CH(Li)C(H)Me2]4.1/2C6H5CH3. The salient feature of their common pseudocubane (LiO)4 tetrameric structure is the presence of both Li-O and Li-C bonding, which is manifested through (LiOPC) chelate rings. Somewhat surprisingly, Li-C bonding is also found in the related hemi-TMEDA solvated complex [{Ph2P(O)CH2Li}2.TMEDA]2. Its tetranuclear structure is, in contrast, best viewed as a dimer of dinuclear units. Ab initio MO calculations have been carried out in order to explain why such Li-C interactions occur and why they can be retained in complexed systems. Chapter 4 describes the solvent-dependent reactions of 1-lithio-methyldiphenylphosphane oxide with tert-butyl cyanide. The products obtained, tetrameric [Ph2P(O)C(H)=C(tBu)N(H)Li]4.1/2C6H5CH3, dimeric [Ph2P(O)C(H)=C(tBu)N(H)Li]2.TMEDA and monomeric Ph2P(OLi)C=C(tBu)NH2.12-crown-4, are the first crystallographically characterised lithiated organophosporous enamines. Interestingly, the unsolvated enamide is found to behave as a C-nucleophile towards methyl iodide but as a N-nucleophile towards methanol or water. Two new sodium azaallyls, [nPrC(H)=C(tBu)N(H)Na.TMEDA]2 and [PhC(H)=C(tBu)N(H)Na.2HMPA]2, are also reported since the nitrile insertion/H-migration process involved in their formation relates closely to that taking place in the formation of the lithium enamides.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available