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Novel group 6 complexes of cyclopentadienylidene ylidesBrownie, John Hugh 12 September 2007 (has links)
Abstract
Methyldiphenylphosphonium cyclopentadienylide, C5H4PMePh2 (II), has been
synthesized and characterized spectroscopically and
crystallographically, and has been found to exhibit properties
consistent with the zwitterionic structure IIb. New group 6
complexes, (η5-C5H4PMePh2)M(CO)3, have been synthesized
and fully characterized. Comparisons of ν(CO) of these complexes with those of the
isoelectronic (η6-C6H6)M(CO)3 and [(η5-C5H5)M(CO)3]- suggest that the electron
donating ability of the ylide is between that of the cyclopentadienyl anion (Cp-) and
benzene, but closer to Cp-. The electronic structures of II and of (η5-
C5H4PMePh2)Cr(CO)3 have been investigated using ab initio methodologies. Thermal
and photochemical substitutions of the CO ligands of (η5-C5H4PMePh2)M(CO)3 (M = Cr,
Mo) by equimolar amounts of PMe3 and PPh3 were not observed, but the ylide is
displaced photochemically from (η5-C5H4PMePh2)Mo(CO)3 by excess PMe3 to form fac-
Mo(CO)3(PMe3)3 while (η5-C5H4PMePh2)Mo(CO)3 reacts with I2 to form [(η5-
C5H4PMePh2)Mo(CO)3I]I.
One electron oxidations of (η5-C5H4PMePh2)M(CO)3 (M = Cr, Mo, W) have been
performed to give the cationic radicals [(η5-C5H4PMePh2)M(CO)3]+, which undergo
dimerization to give dicationic metal-metal bonded dimers ((η5-C5H4PMePh2)M(CO)3)2
2+
in the solid state. These complexes have been fully characterized spectroscopically and
crystallographically. It has been determined that the chromium dimer ((η5-
C5H4PMePh2)Cr(CO)3)2
2+ undergoes dissociation extensively in solution to the persistent
radical cation monomer (η5-C5H4PMePh2)Cr(CO)3
+, but that the heavier metal analogues
iii
((η5-C5H4PMePh2)M(CO)3)2
2+ (M = Mo, W) dissociate very little, if at all. The Cr-Cr
bond distance of the chromium complex is 3.3509(7) Å, which is the longest Cr-Cr bond
distance known for a compound not containing some type of ligand bridging the metalmetal
bond.
The hitherto unknown indenyl-derived ylide, C9H6PMePh2, has been synthesized
and characterized spectroscopically and crystallographically. The chromium tricarbonyl
complex of this ligand, (η5-C9H6PMePh2)Cr(CO)3, has been synthesized and
characterized spectroscopically and crystallographically. This complex is a mixture of
two isomers exhibiting planar chirality generated upon coordination of the ligand. This
complex represents the first structurally characterized phosphorus noncyclopentadienylide
coordinated in an η5 manner. The spectroscopic and crystallographic
behaviour of C9H6PMePh2 demonstrates that this ylide behaves much like the related
cyclopentadienylides. / Thesis (Ph.D, Chemistry) -- Queen's University, 2007-09-07 11:46:39.391
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Novel sugar phosphorus ylides : their synthesis, structure and reactivity : synthesis of a series of sugar-derived phosphorus ylides from protected sugar derivatives and beta-oxo ylides as a route to novel alkynes and trioxo compoundsSahabo, Nina Carole January 2010 (has links)
Higher carbon chain sugars have gained increased interest recently; they are important building blocks of natural and unnatural products with biological properties. The synthesis of these higher sugar skeletons is commonly known to be achieved with the Wittig methodology which exploits phosphorus ylide chemistry. This method has been successfully used for the synthesis of the higher carbon sugars. The aim of this project was to synthesise ß,ß'-dioxo sugar-derived phosphorus ylides, a new class of ylides, as versatile intermediates to valuable higher carbon sugar derivatives and carbohydrate mimics. Model reactions were initially conducted; tetrahydro-2-furoic acid and tetrahydro-2H-pyran-4-carboxylic acid, compounds which are structurally similar to the precursor sugars, were identified as suitable model compounds. These compounds were converted to acyl chlorides and then converted to ß,ß'-dioxo phosphorus ylides precursors by acylation. The methodology proved successful and 8 examples were isolated. However, low yields were obtained due to the inevitable formation of triphenylphosphine oxide. The method was then extended to sugar derivatives, prepared using standard protecting group chemistry. It was found that acylation could be achieved using the simple acyl chloride route or peptide coupling methodology for sugar derivatives which were acid sensitive. ß,ß'-dioxo sugar-derived phosphorus ylides (16 examples) were successfully isolated in low yields. The oxidation and thermal reactivity of the ß,ß'-dioxo ylides were studied. Oxidation resulted in the successful synthesis of vicinal tricarbonyls, isolated as a mixture with the gem-diols (hydrates). The thermal decomposition of the ylides gave alkynes in moderate yields.
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Novel sugar phosphorus ylides: Their synthesis, structure and reactivity. Synthesis of a series of sugar-derived phosphorus ylides from protected sugar derivatives and beta-oxo ylides as a route to novel alkynes and trioxo compounds.Sahabo, Nina Carole January 2010 (has links)
Higher carbon chain sugars have gained increased interest recently; they are important building blocks of natural and unnatural products with biological properties. The synthesis of these higher sugar skeletons is commonly known to be achieved with the Wittig methodology which exploits phosphorus ylide chemistry. This method has been successfully used for the synthesis of the higher carbon sugars. The aim of this project was to synthesise ß,ß'-dioxo sugar-derived phosphorus ylides, a new class of ylides, as versatile intermediates to valuable higher carbon sugar derivatives and carbohydrate mimics.
Model reactions were initially conducted; tetrahydro-2-furoic acid and tetrahydro-2H-pyran-4-carboxylic acid, compounds which are structurally similar to the precursor sugars, were identified as suitable model compounds. These compounds were converted to acyl chlorides and then converted to ß,ß'-dioxo phosphorus ylides precursors by acylation. The methodology proved successful and 8 examples were isolated. However, low yields were obtained due to the inevitable formation of triphenylphosphine oxide.
The method was then extended to sugar derivatives, prepared using standard protecting group chemistry. It was found that acylation could be achieved using the simple acyl chloride route or peptide coupling methodology for sugar derivatives which were acid sensitive. ß,ß'-dioxo sugar-derived phosphorus ylides (16 examples) were successfully isolated in low yields.
The oxidation and thermal reactivity of the ß,ß'-dioxo ylides were studied. Oxidation resulted in the successful synthesis of vicinal tricarbonyls, isolated as a mixture with the gem-diols (hydrates). The thermal decomposition of the ylides gave alkynes in moderate yields.
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Développement d'une nouvelle méthodologie d'oléfination catalysée par les complexes de cuivre : applications dans des réactions en tandemDavi, Michaël January 2008 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.
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Développement d'une nouvelle méthodologie d'oléfination catalysée par les complexes de cuivre : applications dans des réactions en tandemDavi, Michaël January 2008 (has links)
Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal
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