Spelling suggestions: "subject:"cobalt"" "subject:"kobalt""
171 |
Complexes de fer(II) et de cobalt(II) de basse coordinance : synthèses, caractérisations et applications en réaction d’hydroamination des alcènes / Low valence iron(II) and cobalt(II) complexes : synthesis, characterisations and applications in alkenes hydroamination reactionLepori, Clément 08 December 2017 (has links)
Les motifs azotés sont présents dans de nombreuses molécules d’intérêts pharmaceutiques. Les méthodes de synthèses traditionnelles de ces motifs vont, par exemple, de la substitution nucléophile d’amines sur des halogénures d’alkyles à de l’amination réductrice des composés carbonylés. Ces méthodes, bien qu’efficaces, nécessitent néanmoins des quantités stœchiométriques de réactifs pour être appliquées et génèrent souvent des quantités importantes de déchets. Un des challenges de la chimie organique moderne consiste à développer de nouvelles méthodes de synthèses de ces motifs plus économiques et plus respectueuses de l’environnement en produisant un taux de déchets le plus faible possible. L’addition directe d’une amine sur une double liaison carbone-carbone non-activée que l’on appelle la réaction d’hydroamination des alcènes est une approche très prometteuse pour le développement d’une méthodologie de synthèse alternative de ces composés. En effet, dans cette réaction, tous les atomes du substrat de départ sont transférés au produit réduisant ainsi considérablement les déchets produits. De plus, les amines et les oléfines employées sont des réactifs relativement bon marché, abondants et variés. Néanmoins, cette transformation a priori simple nécessite généralement l’emploi d’un catalyseur. Dans la littérature, la réaction d’hydroamination des alcènes a été étudiée en utilisant comme catalyseur des complexes de métaux alcalins, alcalino-terreux, de terre-rares et de métaux de transition. Au commencement de ce projet, il n’existait pas d’exemples de réaction d’hydroamination des alcènes mettant en jeu des amines primaires non protégées catalysée par des complexes de fer ou de de cobalt. Dans ce contexte, notre équipe s’est intéressée à la réactivité de complexes de fer(II) et de cobalt(II) de basse valence stabilisés par des ligands de type β-dicétiminate. Ces complexes se sont révélés être d’excellents catalyseurs pour promouvoir la réaction d’hydroamination des amines primaires non protégées liées à des alcènes non activés.Dans un premier temps, les synthèses des complexes de fer(II) et de cobalt(II) alkyles stabilisés par des ligands β-dicétiminates ainsi que leurs applications en réaction de cyclohydroamination des amines primaires non protégées seront présentées. De plus, des études mécanistiques poussées permettront d’éclaircir le mécanisme de la réaction, qui est proposé de passer par une étape élémentaire clé d’insertion 1,2 migratoire aboutissant à la formation d’une liaison carbone-azote.Dans un second temps, les influences des propriétés électroniques et stériques des ligands sur la réactivité en réaction d’hydroamination des alcènes des complexes de fer(II) alkyles seront étudiées. Nous nous attarderons particulièrement sur des complexes stabilisés par des ligands β-dicétiminates dissymétriques ou iminoanilidures. Les données cristallographiques des complexes à l’état solide permettront alors de rationaliser les variations de réactivités de ces différents complexes.Enfin, les complexes de fer(II) et de cobalt(II) synthétisés précédemment seront exploités pour développer de nouvelles réactivités en réactions d’oxydation, d’amination oxydante ou de création de liaison azote-silicium par un couplage déshydrogénant. / The nitrogenous units are present in many molecules of pharmaceutical interest. The traditional synthesis methods of these units range, for example, from the nucleophilic substitution of amines on alkyl halides to reductive amination of the carbonyl compounds. These methods, although effective, nevertheless require stoichiometric amounts of reagents to be applied and often generate large amounts of waste. One of the challenges of modern organic chemistry is to develop new methods of synthesizing these more economical and environmentally friendly patterns by producing the lowest waste rate possible. The direct addition of an amine to an unactivated carbon-carbon double bond known as the alkene hydroamination reaction is a very promising approach for the development of an alternative synthesis methodology for these compounds. Indeed, in this reaction, all the atoms of the starting substrate are transferred to the product thus considerably reducing the waste produced. In addition, the amines and olefins employed are relatively inexpensive, abundant and varied reagents. Nevertheless, this simple transformation generally requires the use of a catalyst. In the literature, the hydroamination reaction of alkenes has been studied using alkali metal, alkaline earth, rare earth and transition metal complexes as catalysts. At the beginning of this project there were no examples of the hydroamination reaction of alkenes involving unprotected primary amines catalysed by iron or cobalt complexes. In this context, our team was interested in the reactivity of iron (II) and cobalt (II) complexes of low valence stabilized by β-diketiminate ligands. These complexes have proved to be excellent catalysts for promoting the hydroamination reaction of unprotected primary amines bound to non-activated alkenes.In a first step, the syntheses of the iron (II) and cobalt (II) complexes stabilized by β-diketiminate ligands as well as their applications in cyclohydroamination reaction of the unprotected primary amines will be presented. In addition, advanced mechanistic studies will clarify the mechanism of the reaction, which is proposed to go through a key elementary 1..2 migratory insertion leading to the formation of a carbon-nitrogen bond.In a second step, the influence of the electron and steric properties of the ligands on the reactivity in the hydroamination reaction of the alkenes of the iron (II) alkyl complexes will be studied. We will focus particularly on complexes stabilized by asymmetric β-diketiminate ligands or iminoanilides. The crystallographic data of the solid state complexes will then make it possible to rationalize the variations of reactivities of these various complexes.Finally, the iron (II) and cobalt (II) complexes synthesized above will be exploited to develop new reactivities in oxidation reactions, oxidative amination or the creation of a nitrogen-silicon bond by a dehydrogenating coupling.
|
172 |
Characterisation and Solution Chemistry of N-Acetyl-Cobalt(III)-Microperoxidase 8Sannasy, Desigan 14 February 2007 (has links)
Student Number : 0010064D -
MSc dissertation -
School of Chemistry -
Faculty of Science / This dissertation describes the synthesis, physical characterisation and solution chemistry
of NAc-CoIIIMP8, a biomimetic model compound of vitamin B12a, synthesised from the
haemoctapeptide derived from horse heart cytochrome c. Peptic and tryptic digestion of
horse heart cytochrome c removes much of the globular protein encapsulating the iron
porphyrin prosthetic group. The resulting haemoctapeptide fragment retains residues 14
to 21 of the parent cytochrome (MP8) via thioether linkages to Cys-14 and Cys-17.
Reductive demetalation of MP8 yielded the metal free MP8. This was treated with
cobaltous acetate in an aerated aqueous solution to produce CoIIIMP8. CoIIIMP8 was
acetylated by treatment with acetic anhydride and yielded N-acetyl-Co(III)-
microperoxidase 8 (NAc-CoIIIMP8). It is well established that acetylation reduces
aggregation of these haempeptides. The starting materials and products of each step
during synthesis were characterised by UV-visible absorption spectroscopy, high
performance liquid chromatography (HPLC) and fast atom bombardment-mass
spectroscopy (FAB-MS). MP8 free base and Co(III)-MP8 were also analysed using
luminescence spectroscopy.
The molar extinction coefficients of NAcCoIII-MP8 in aqueous and ionic medium were
determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES)
and UV- visible absorption spectroscopy. The extinction coefficient, e, of NAcCoIIIMP8
(? = 420 nm, pH 7.00, 25 ºC) in distilled water and 1.0 M NaClO 4 was 1.80 + 0.01 x 105
M-1 cm-1 and 1.66 + 0.01 x 105 M-1 cm-1, respectively. Beer’s law studies show that
NAc-CoIIIMP8 remains monomeric in aqueous solution up to concentrations of at least 35
μM.
The spectroscopic changes observed for NAc-CoIIIMP8 during the course of a
spectrophotometric titration are very similar to those observed for NAc-FeIIIMP8, with
both being consistent with six successive ionisations. By analogy with NAc-FeIIIMP8,
we attributed the first (pK1 = 2.0 + 0.3) to the coordination of the c-terminal carboxylate
group (Glu-21) of the appended polypeptide. The second acid range transition (pK2 = 2.8 + 0.1) for NAcCoIIIMP8 involved the deprotonation of the cationic His-18 and
concomitant replacement of the c-terminal carboxylate by the neutral heterocyclic base.
The third and fourth pKa’s are attributed to the ionisation of the haem propanoic acid
groups (pK3 = 3.9 + 0.03) and (pK4 = 7.5 + 0.03). Ionisation of the cobalt-bound water
molecule above neutal pH was assigned to pK5 = 9.2 + 0.04. Finally, we attributed pK6
(12.1 + 0.03) to the ionisation of the coordinated histidine trans to the OH- to form the
histidinate complex (His--CoIII-OH-).
A principal aim of this work was to demonstrate that the kinetics and the thermodynamics
of the ligand substitution reactions of NAc-CoIIIMP8 can be studied
spectrophotometrically; a comprehensive investigation of these reactions will be
undertaken by othe rs. Towards this end the formation constants between NAc-CoIIIMP8
and N- methylimidazole and pyridine were determined. We observed the formation of a
bis-substituted complex in the reaction of NAc-CoIIIMP8 with the ligands, but only
mono-substitution with NAc-FeIIIMP8 and B12a. We attribute this first ligand binding to
the replacement of the axial water molecule, and the second replacement of the axial
histidine residue. The absence of the second reaction with NAc-FeIIIMP8 and B12a
suggest that the CoIII-N(His) bond in NAc-CoIIIMP8 is significantly weaker than the FeIIIN(
His) and CoIII-N(dimethylbenzimidazole) bond, respectively. When comparing the
formation constants of NAc-FeIIIMP8, NAc-CoIIIMP8 and B12a, we found that the value
of log K1 for NAc-CoIIIMP8 for these ligands is significantly higher than that reported for
NAc-FeIIIMP8 and B12a.
Kinetics studies of NAc-CoIIIMP8 with N-methylimidazole and methylamine were
investigated. The data obtained did not follow conventional pseudo-first order kinetics;
instead there was some evidence for biphasic kinetics. In the reaction of Nmethylimidazole
with NAc-CoIIIMP8, we observed that the rate of reaction is virtually
independent of the concentration of the incoming ligand. The results can be explained if
the mechanism proceeds through a purely dissociative mechanism, i.e., if the rate of the
reaction is controlled by the rate at which, firstly, the water molecule dissociates from the
CoIII centre and, secondly, the histidine dissociates from the metal. The second order rate constant, k2, could not be determined since the rate of reaction is independent of Nmethylimidazole
concentration. In the reaction of methylamine with NAc-CoIIIMP8, we
observed that the rate of reaction is dependent on the concentration and participation of
the incoming ligand. We propose that the displacement of water and histidine by
methylamine involves an interchange mechanism (Id), where the bond forming and bond
breaking occur simultaneously, and thus the rate of reaction becomes dependent on the
concentration of the incoming ligand.
The results showed that the rate of reaction for methylamine with NAc-CoIIIMP8 was
faster than with N-methylimidazole. We attributed these differences in rate constants to
the size of the incoming ligands. N-methylimidazole is a secondary amine and is
relatively more bulky than methylamine which is a primary amine; therefore it is easier
for methylamine to attach to the metal centre compared to N- methylimidazole.
For comparison, the rate of reaction of B12a with N-methylimidazole and methylamine
was determined. The results show that the rate of the reaction between NAc-CoIIIMP8
and B12a with N-methylimidazole and methylamine are significantly different.
Furthermore, we observe only mono -substitution in B12a and bisubstitution in NAc-
CoIIIMP8. Overall, the results presented in this work do give a general indication on how
thermodynamically stable a CoIII ion is in a porphyrin ring and also to a very limited
extent show that a porphyrin does not confer the same kinetic lability on the CoIII ion as
the corrin ring.
|
173 |
First-Principles Study of Ethanol and Methanol Steam Reforming on Co-based MaterialsLuo, Wenjia 22 May 2015 (has links)
No description available.
|
174 |
Growth, dislocations, and extinction of cobalt whiskersBailey, Billy Hugh. January 1964 (has links)
Call number: LD2668 .T4 1964 B15 / Master of Science
|
175 |
SYNTHESIS, CHARACTERIZATION AND REACTIONS OF TERTIARY PHOSPHINE COMPLEXES OF COBALT DERIVATIVES OF NITROGEN OXIDES.VALLENILLA, CLEMENTE DIOGENES. January 1985 (has links)
Co(NO)(NO₂)₂L₂ complexes (L = PPh₃, PMePh₂, PMe₂Ph, PMe₃, PEt₃, PEt₂Ph, PEtPh₂, PPrPh₂, PBu₃ and 1/2DPPPr) were prepared from the reactions of Co(NO)X₂L₂ (X = Cl, Br) with sodium nitrite in methanol freshly distilled from magnesium methoxide. The complexes were characterized by elemental analysis, 15-N labeling, infrared and NMR spectroscopy. The crystal structure of Co(NO)(NO₂)₂(PMePh₂)₂ was determined by X-ray diffraction. The cobalt atom has tetragonal pyramidal geometry. The nitrosyl group in the axial position is strongly bent. The NO₂ ligands have two different ligating geometries: one is bound to cobalt through the nitrogen atom and the other is bidentate forming an asymmetric four membered ring. The phosphine ligands are equivalent and trans to each other. Multinuclear NMR spectroscopy (¹H, ³¹P, ¹⁵N and ¹⁴N) was used to determine the solution structure of Co(NO)(NO₂ )₂L₂ complexes, to study mono and bisnitrosyls of cobalt, to establish some correlations between NMR parameters and structural characteristics of these complexes and to follow their reactions in solution. Reactions of Co(NO)(NO₂)₂L₂ with CO, NO and RCOX were observed to produce Co(NO)₂XL complexes. Since the structure may be indicative of electronic requirements at the metal center as well as the reactivity of the compounds, The crystal structures of Co(NO)₂Cl(PPh₃) and Co(NO)₂(ONO)(PPh₃) were also determined. In these complexes the cobalt atoms have pseudotetrahedral geometry. The CoNO angles are in the range considered to be linear. They are geniculated in an "atracto" conformation. Co(NO)(NO₂)₂L₂ and Co(NO)₂(ONO)L complexes react with oxygen in the solid state or in solution to form Co(NO₃)₂(OL)₂ complexes. When the reactions with O₂ were carried out in the presence of an excess of olefins, the formation of nitrates is inhibited Co(NO₂)₂(OL)₂ and olefin oxides are formed instead. The crystal structures of Co(NO₃)₂(OPMePh₂)₂ and Co(NO₂)₂(OPMePh₂)₂ were determined by X-ray diffraction. In these complexes, the NO₃ and NO₂ groups are bidentate. They are arranged in a cis configuration around the cobalt atom.
|
176 |
The kinetics and mechanism of substitution in some cobalt (III) complexes梁秉元, Leung, Ping-yuen. January 1969 (has links)
published_or_final_version / Chemistry / Master / Master of Science
|
177 |
Influence of the nephelauxetic effect on the kinetic and thermodynamicstability of cobalt (III) complexes of the tetramine typeTong, Ha-wai, 唐夏維 January 1973 (has links)
published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy
|
178 |
Spectral and kinetic studies of some octahedral cobalt (III)complexes李子健, Lee, Chi-kin. January 1973 (has links)
published_or_final_version / Chemistry / Master / Master of Science
|
179 |
EXAFS studies on transition metal complexesWardell, E. M. January 1986 (has links)
No description available.
|
180 |
New models for coenzyme Bâ†1â†2-dependent reactionsGarnett, Ian January 1995 (has links)
No description available.
|
Page generated in 0.0248 seconds