Environmental concerns have birthed an awareness of how we conduct ourselves as citizens of this planet. To reduce environmental impact, we have learned that we must be responsible stewards in all ranges of life: from buying locally grown food to how scientific research and industrial processes are executed. In the realm of chemical research, "green chemistry" has initiated the development of new, sustainable methods that make use of atom economy, step economy, and utilize renewable materials to minimize waste and production of toxic by-products. The formation of carbon-carbon bonds lies at the very heart of organic synthesis, and traditional methods for forming such bonds generally require the use of at least one stoichiometrically preformed organometallic reagent. This corresponds to at least one equivalent of metallic waste byproduct. The in situ formation of alkyl metal nucleophiles for carbonyl additions via hydrogenation of [pi]-unsaturates represents an alternative to use of preformed organometallic reagents. Comprising nearly 90% of the atoms in the universe, hydrogen is vastly abundant and very cheap. The Krische group seeks to contribute new technologies which make use of catalytic hydrogenation and transfer hydrogenation in the reductive coupling of basic chemical feedstocks. / text

By simply hydrogenating enones in the presence of aldehydes at ambient temperature and pressure, aldol adducts are generated under neutral conditions in the absence of any stoichiometric byproducts. Using cationic rhodium complexes modified by tri(2-furyl)phosphine, highly syn-diastereoselective reductive aldol additions of vinyl ketones are achieved. Finally, using novel monodentate TADDOL-like phosphonite ligands, the first highly diastereo- and enantioselective reductive aldol couplings of vinyl ketones were devised. These studies, along with other works from our laboratory, demonstrate that organometallics arising transiently in the course of catalytic hydrogenation offer byproduct-free alternatives to preformed organometallic reagents employed in classical carbonyl addition processes. Existing methods for enantioselective carbonyl allylation, crotylation and tert-prenylation require stoichiometric generation of pre-metallated nucleophiles, and often employ stoichiometric chiral modifiers. Under the conditions of transfer hydrogenation employing an ortho-cyclometallated iridium C,O-benzoate catalyst, enantioselective carbonyl allylations, crotylations and tert-prenylations are achieved in the absence of stoichiometric metallic reagents or stoichiometric chiral modifiers. Moreover, under transfer hydrogenation conditions, primary alcohols function dually as hydrogen donors and aldehyde precursors, enabling enantioselective carbonyl addition directly from the alcohol oxidation level. / text

LD2668 .T4 1966 T458 / Master of Science

This thesis describes the developments of new protocols for the hydrogenation of challenging substrates. Three specific substrates were highlighted for study after an initial review of the literature; benzofurans, esters and bulky ketones. Chapter 1 details a review of the hydrogenation of challenging unsaturated substrates, highlighting areas where development is still required. Chapter 2 describes studies on the hydrogenation of 2,3-benzofuran. While a benzofuran hydrogenation catalysts was optimised, severe conditions were required to facilitate the reaction, and not found to be applicable for more elaborate substrates. We therefore considered an alternative process of enantioselective hydrogenation of benzofuranyl ketones followed by heterogeneous hydrogenation. A good process for transfer hydrogenation of a range of these hitherto unstudied substrates was developed along with greater understanding. The hydrogenation of esters is another challenge in the catalytic reduction field, so was also selected for study, with the results described in Chapter 3. After screening a range of catalysts of types [RuCl₂ (diphosphine)(diamine)] and [RuCl₂ (PNX)(DMSO)], good catalysts were identified. Successful hydrogenation of a range of esters, under mild conditions was achieved using [RuCl₂ (1,3-bisdiphenylphosphinepropane)(2-aminomethylpyridine)] using high concentrations of base co-catalyst. [RuCl₂ ((2-(diphenylphosphanylbenzyl)ethane-1,2-diamine)(DMSO)] combined with 15-25 mol% of a basic co-catalyst have been shown to be active at near ambient conditions in the hydrogenation of aromatic esters. Chapter 4 related to studies where the activity of Ru, Ir and Rh complexes of the same tridentate ligand were tested in the hydrogenation of ketones that would be regarded as sluggish substrates. Highly active and selective catalysts for the hydrogenation of bulky acetophenone derivatives were found using iridium complexes of PNX ligands (formed in situ). The highest selectivity was obtained with acetophenone substrates containing iso-propyl and cyclohexyl substituents, or medicinally important piperdinyl groups. In the best cases over 90% e.e. was observed with high conversions and with only 0.1 mol% of catalyst.

No description available.

Les alliages de titane possèdent une faible activation neutronique, une bonne tenue mécanique et une bonne résistance à la corrosion de manière générale. Ils sont susceptibles d’être utilisés comme matériau de structure de composants du circuit primaire des réacteurs nucléaires à eau pressurisée. Cette étude s’intéresse à leur durabilité dans ce milieu.Des échantillons de trois alliages de titane alpha (T40), alpha + beta (TA6V) et beta métastable (Ti10­-2-­3) ont été exposés au milieu primaire à 300 °C et à 350 °C pour des durées maximales de 11000 h et 1750 h respectivement. Des observations MEB et des analyses XPS, SDL, MET-ASTAR et de photoélectrochimie ont permis de proposer un mécanisme de corrosion impliquant simultanément la croissance interne et la dissolution dans le milieu d’une fine couche dense de TiO2 accompagnées de la précipitation de cristallites d’oxydes TiO2 et FeTiO3 liée à la saturation du milieu en hydroxydes. Il en résulte une consommation du métal estimée grâce à des analyses d’images et à la modélisation des prises de masse en fonction du temps de 2,9 µm.an­-1 à 300 °C et de 18 µm.an-­1 à 350 °C au maximum. Cette cinétique de corrosion est fortement ralentie lorsque les cristallites de FeTiO3 recouvrent la totalité de la surface des échantillons. L’exposition au milieu primaire des matériaux implique aussi une prise d’hydrogène d’autant plus importante que la température et le taux de phase beta sont élevés. Des essais de traction à température ambiante ont été réalisés sur des éprouvettes exposées au milieu primaire et sur des éprouvettes chargées en hydrogène ou traitées thermiquement. Ces essais ont mis en évidence une baisse de ductilité du Ti10­2­3 liée à son exposition au milieu primaire. Cette baisse de ductilité semble résulter de l’effet couplé du vieillissement thermique et de la présence d’hydrures aux interfaces alpha/beta. L’exposition au milieu primaire réalisée au laboratoire du T40 et du TA6V ne modifie que très peu leurs propriétés mécaniques étant donné que les prises d’hydrogène sont faibles devant les concentrations en hydrogène de transition ductile/fragile.L’utilisation des alliages de titane en milieu primaire paraît donc possible sur de longues durées sous réserve que leur phase beta soit stable et que les pièces possèdent un rapport surface/volume suffisamment faible pour limiter leur teneur en hydrogène. / Titanium alloys have a low neutron activation, good mechanical properties and good corrosion resistance in common environment. They could be good candidates for nuclear Pressurised Water Reactor (PWR) primary circuit structure components. This study deal with their durability in primary water.Samples of three titanium alloys alpha (Ti CP), alpha + beta (Ti 64) and metastable beta (Ti10­2­3) were exposed to primary water at 300 °C and 350 °C for maximum durations of 11000 h and 1750 h, respectively. Based on SEM observations as well as XPS, GD-OES, MET-ASTAR and photoelectrochemistry analysis, a corrosion mechanism was proposed. It involves the inward growth of a dense TiO2 layer and its simultaneous dissolution into primary water as well as TiO2 and FeTiO3 oxide crystallites precipitation. Image analysis and mass uptake modelling indicated a maximum resulting metal matrix corrosion rate of 2.9 µm.year-­1 at 300 °C and of 18 µm.year-­1 at 350 °C. An abrupt decrease of the corrosion rate was noticed as FeTiO3 oxide crystallites surface covering fraction reached 100 %. Materials exposure to primary water also led to a hydrogen uptake which increased with both temperature and beta phase ratio. Room temperature tensile tests were performed on primary water exposed specimens, hydrogen charged specimens and heat treated specimens. These tests highlighted a loss of ductility of Ti10­2­3 samples linked to their exposure to primary water. It could be due to the combined effects of both thermal ageing and hydride presence at alpha/beta interfaces. Primary water exposure performed in laboratory had little effect on T40 and TA6V mechanical properties because hydrogen uptake is low in comparison with hydrogen concentration leading to ductile/brittle transition.Long duration use of titanium alloys in primary water seems reasonable, provided that beta phase is stable and that the surface/volume ratio of the considered component is low enough.

Transfer hydrogenation has been recognized to be an important synthetic method in both academic and industrial research to obtain valuable products including alcohols. Transition metal catalysts based on precious metals, such as Ru, Rh and Ir, are typically employed for this process. This thesis starts with a study on the potential of an Fe based complex carrying a PNP ligand (2,6-{Ph2PNH}2(NC5H3)) to function as an active transfer hydrogenation catalyst for the conversion of ketones to alcohols. During the analysis of the performance parameters of this potential catalyst, it was discovered that the added base, KOtBu, was the actual catalyst. Other bases were explored as catalysts for this transformation as well as the general performance features of this simple alkali metal base. In a separate project described in Chapter 3, the search for catalysts shifted focus to a study of the potential of a series of first row transition metal-based complexes supported by a bis(thioether)pyridine “SNS” ligand for photocatalytic hydrogen production. This initial study led to the observation that the Fe complex [Fe(k3-2,6-(CH3SCH2)2C5H3N)Br2]2 was a capable photocatalyst for H2 production in combination with a photosensitizer (Ru(bpy)3)2+) and an electron donor (triethanolamine). Although water was initially believed to be the source of protons that were reduced to H2, analysis of control experiments pointed to the hydrogen source being the electron donor.

The ligand tBu2PC2H4NHCH2Py (PNHN) was synthesized starting from 2-pyridinecarboxaldehyde and 2-chloroethanamine. Initial attempts for coordination of the PNHN ligand to a metal center was performed using [IrCl(COE)2]2, IrCl3·3H2O, [RuCl2(p-cymene)]2 and RuCl2(PPh3)3. The reaction between the PNHN ligand and [IrCl(COE)2]2 under H2 resulted in the chloride IrCl(H)2(PNHN). Synthesis of the active hydride species is currently under investigation. A reaction of the PNHN ligand with RuCl2(PPh3)3 under nitrogen afforded the dichloride RuCl2(PPh3)(PNHN). Treatment of the dichloride with KOBut in 2-pentanol led to the formation of the dihydride RuH2(PPh3)(PNHN). Formation of the 16-electron amido complex RuH(PPh3)3(PNN) was achieved through the evolution of H2. The dihydride demonstrated good potential catalytic activity for transfer hydrogenation of acetophenone and cyclohexanone. Current work involves the synthesis of a chiral analogue of the PNHN ligand.

The ligand tBu2PC2H4NHCH2Py (PNHN) was synthesized starting from 2-pyridinecarboxaldehyde and 2-chloroethanamine. Initial attempts for coordination of the PNHN ligand to a metal center was performed using [IrCl(COE)2]2, IrCl3·3H2O, [RuCl2(p-cymene)]2 and RuCl2(PPh3)3. The reaction between the PNHN ligand and [IrCl(COE)2]2 under H2 resulted in the chloride IrCl(H)2(PNHN). Synthesis of the active hydride species is currently under investigation. A reaction of the PNHN ligand with RuCl2(PPh3)3 under nitrogen afforded the dichloride RuCl2(PPh3)(PNHN). Treatment of the dichloride with KOBut in 2-pentanol led to the formation of the dihydride RuH2(PPh3)(PNHN). Formation of the 16-electron amido complex RuH(PPh3)3(PNN) was achieved through the evolution of H2. The dihydride demonstrated good potential catalytic activity for transfer hydrogenation of acetophenone and cyclohexanone. Current work involves the synthesis of a chiral analogue of the PNHN ligand.

The catalytic hydrogenation of an aromatic sulfonyl chloride was investigated in continuous and semi-batch mode processes using a Robinson-Mahoney stationary basket reactor. A complete experimental unit was designed and built. The operating and analytical procedures have been developed and the methodologies to gather the kinetic data have been described. Hydrogenation reactions were conducted at a reaction pressure of 364.7 psia, at three different reaction temperatures: 85 °C, 97 °C and 110 °C, at five different residence times: 0.6 (only at 110 °C), 1.0, 1.5, 2.0, 3.1 hr, with the hydrogen to the aromatic sulfonyl chloride molar ratio: 8.0 mol/mol and hydrogen to argon molar ratio: 3.0 mol/mol. Intrinsic reaction rates of the reacting species were obtained on the surface of a commercial 1 wt% palladium on charcoal catalyst. The conversion and molar yield profiles of the reacting species with respect to process time suggest a deactivation of the 1 wt % palladium on charcoal catalyst. Kinetic data collected in a continuous process mode show that the catalyst is deactivated during an experiment when the process time equal to two to three times the residence time of the liquid within the reactor. XRD analysis shows that the active sites are blocked and an amorphous layer was formed on the surface of the palladium catalyst. Semi-Batch mode experimental data were obtained at 110 °C after 8 hours of reaction time for several aromatic sulfonyl chlorides. A kinetic model has been developed, which includes adsorption of individual components and surface reactions as well as rate equations of the Hougen-Watson type. A hyperbolic deactivation function expressed in term of process time is implemented in the Hougen-Watson equation rates. The mathematical model consists of non-linear and simultaneous differential equations with multiple variables. The kinetic parameters were estimated from the minimization of a multi-response objective function by means of a sequential quadratic program, which includes a quasi-Newton algorithm. The statistical analysis was based on the t- and F-tests and the simulated results were compared to the experimental data.