Chapter one is an introduction, outlining the structure and bonding of N-heterocyclic carbenes (NHCs). It then goes on to give examples of f -metal NHC complexes and describes any reactivity or catalytic activity. Chapter two describes the synthesis of the transition metal NHC complexes [Fe (LMes)2] 3 and [Co(LMes)2] 4 (LMes = OCMe2 CH2(1-C{NCH2CH2NMes})). The heterobimetallic complexes [(LMes)Fe(μ-LMes)U(μ-{N(SiMe3)Si(Me)2CH2})(N(Si Me3)2)2] 5 and [(LMes)Co(μ-LMes)U(μ-{N(SiMe3)Si(Me)2CH2})(N(SiMe3)2)2] 6 were prepared from the reaction between [({Me3Si}2N)2U(NSiMe3SiMe2CH2)] and 3 or 4, respectively. Complex 5 was also synthesised by the reaction between 3 and [U(N{SiMe3}2)2]. The diamagnetic analogue [(LMes)Zn(μ-LMes)Th(μ-{N(SiMe3)Si (Me)2CH2})(N(SiMe3)2)2] 9 was prepared from the reaction between [Zn(LMes)2] and [({SiMe3}2N)2Th(NSiMe3SiMe2CH2)]. The reactivity of 5 is discussed. When 5 was reacted with 2,6-dimethylphenyl isocyanide, [({SiMe3}2N)2U{N(SiMe3)Si(Me2)C(CH2)N(2,6−Me−C6H3)}] 8 was isolated. The reaction with CO resulted in the formation of [({Me3Si}2N)2U{N(SiMe3) Si(Me2)C(CH2)CO}]. 5 showed no reactivity with azides, boranes or m-chloroperbenzoic acid and decomposed when exposed to H2, CO2 or KC8. The reaction between 6 and 2,6-di-tert-butylphenol formed the previously reported monometallic complex [({SiMe3}2N)2U(OC6H3tBu2)]. The serendipitous synthesis of the iron ate complex [Na(Fe{LMes}2)2]+ [Fe(ArO)3]– 10 (Ar = 2,6-tBu-C6H3) is also described. Chapter three describes the synthesis of the aryloxide complexes [HC(3-tBu-5-Me- C6H2OH)(3-tBu-5-Me-C6H2O)μ-(3-tBu-5-Me-C6H2O)Co(THF)]2 11 and [HC(3- tBu-5-Me-C6H2OH)(3-tBu-5-Me-C6H2O)μ-(3-tBu-5-Me-C6H2O)Zn(THF)n] 13. Treatment of 11 with pyridine N-oxide resulted in the formation of the pyridine-Noxide adduct [HC(3-tBu-5-Me-C6H2OH)(3-tBu-5-Me-C6H2O)μ-(3-tBu-5-Me-C6H2 O)Co(C5H5NO)]2 12. When 11 was treated with [({Me3Si}2N)2U(NSiMe3SiMe2C H2)], no reaction occured at room temperature but at 80◦C decomposition occured. When 11 was treated with [(NH4)2Ce(NO3)6] the protonated proligand HC(3-tBu- 5-Me-C6H2OH)3 reformed. The reactivity of 11 with [({Me3Si}2N)Ce(LiPr)2] is also discussed. Chapter three also discusses the preparation of the heterobimetallic complex [HC(3- tBu-5-Me-C6H2O)2-μ-(3-tBu-5-Me-C6H2O)KCo]2 14 and the salt-elimination chemistry of the complex. The preparation of [HC(3-tBu-5-Me-C6H2O)2-μ-(3-tBu-5- Me-C6H2O)KZn]2 15 is also outlined. Chapter four discusses the reactivity of [Ce(LiPr)3] (Li Pr =OCMe2CH2(1-C{NCHC HNiPr})) in C-H and N-H activation and as a catalyst for organic reactions. [Ce(LiPr)3] displayed no C-H activation chemistry with RC−−−CH (R = SiMe3, Ph, tBu), diphenyl acetone, indene or fluorene. [Ce(LiPr)3] also showed no N-H activation chemistry with pyrrole or indole, nor did it react with the lignin model compound PhOCH2Ph. When treated with an excess of benzyl chloride, [Ce(LiPr)3] underwent ligand decomposition to form the acylazolium chloride [(C6H5C(O))OCMe2CH2(1-C(C6H5C (O)){NCHCHNiPr})]Cl 18 and CeCl3. When [Ce(LiPr)3] was added to a mixture of benzaldehyde and benzyl chloride, as a coupling catalyst, the complex decomposed. [Ce(LiPr)4] was tested as a catalyst from the benzoin condensation and for the coupling of benzalehyde and benzyl chloride, however, it resulted in the decomposition of [Ce(LiPr)4]. Chapter four also outlines the catalytic activity of 3. The complex showed no reactivity as a hydrogenation catalyst towards alkenes, aldehydes or ketones but did display reactivity as a hydroboration catalyst for alkenes, aldehydes or ketones. Chapter five presents the conclusions for chapters two to four. The final chapter contains the experimental details from the previous chapters.

Dans cette thèse, la synthèse, la caractérisation et les applications en catalyse de nanoparticules mono- et bimétalliques à base de rhodium sont décrites. Le rhodium a été choisi comme métal central de cette étude en raison de son intérêt reconnu en catalyse, principalement pour les réactions d'hydrogénation et d'hydroformylation. La synthèse de nanoparticules de rhodium monométalliques constitue le coeur de ce travail. Elle a été réalisée par décomposition du complexe organométallique [Rh(C3H5)3] en solution, sous pression de dihydrogène et en présence de différents stabilisants tels que des ligands et des polymères pour contrôler la croissance des particules. Certaines nanoparticules ont été déposées sur la surface d'une silice magnétique fonctionnalisée par des groupements amines utilisée comme support, dans un objectif de récupération plus aisée pour le recyclage des catalyseurs. Diverses nanoparticules bimétalliques ont également été préparées par co-décomposition du complexe [Rh(C3H5)3] avec d'autres précurseurs organométalliques, incluant [Ni(cod)2], [Ru(cod)(cot)], [Pt(nor)3] et [Pd(dba)2]2. En modulant les ratios de métaux entre [Rh] et le second métal [M], ainsi que la nature et la quantité de stabilisant utilisé pour la synthèse, des nanoparticules de tailles et de compositions chimiques différentes ont pu être obtenues. La caractérisation des nanoparticules ainsi préparées a été menée en utilisant une combinaison de techniques de l'état de l'art (TEM, HRTEM, STEM-EDX, ICP, WAXS, EXAFS, XANES, XPS, RMN ...). Pour certaines nanoparticules de rhodium, des études de surface ont été réalisées, par adsorption du CO sur la surface des particules et un suivi par des techniques spectroscopiques (FT-IR, RMN) pour sonder leur état de surface. Un autre aspect de ce travail a concerné l'évaluation des nanoparticules synthétisées dans des réactions catalytiques, en particulier réactions d'hydrogénation avec des particules monométalliques de Rh et réaction d'hydrogénolyse avec des nanoparticules bimétalliques RhNiOx. Dans le cas de la catalyse d'hydrogénation, des études en conditions colloïdales et supportées ont été réalisées. L'originalité de ce travail réside dans le développement d'outils de synthèse simples inspirés de la chimie organométallique pour obtenir des nanoparticules à base de rhodium bien contrôlées en termes de taille, distribution en taille, composition et état de surface, tous ces paramètres étant importants quelle que soit l'application visée. L'intérêt des nanoparticules obtenues en catalyse a également été mis en évidence dans différentes réactions. Ce travail de thèse offre de nouvelles opportunités de recherche, tant en nanochimie qu'en catalyse. / In this thesis, synthesis, characterization and catalytic applications of mono- and bi-metallic rhodium-based nanoparticles are reported. Rhodium has been chosen as a primary metal given its high interest in catalysis, mainly in hydrogenation and hydroformylation reactions. The synthesis of mono-metallic rhodium nanoparticles (NPs) is the core of this work. It was performed by decomposition of the organometallic complex [Rh(C3H5)3] in solution under dihydrogen pressure and in the presence of different stabilizers including ligands and polymers to control the growth of the particles. Selected nanoparticles were deposited on the surface of amino-functionalized magnetic silica as a support for recovery and recycling concerns in catalysis. Diverse bi-metallic nanoparticles have been also prepared in one-pot conditions by co-decomposition of the [Rh(C3H5)3] with other organometallic precursors including [Ni(cod)2], [Ru(cod)(cot)], [Pt(nor)3] and [Pd(dba)2]2. Tuning of the metal ratios between [Rh] and the second metal [M], or of the nature and the amount of the stabilizer used for the synthesis allowed to obtain nanoparticles of different sizes and chemical compositions. The characterization of the obtained nanoparticles was performed by using a combination of state-of-art techniques (TEM, HRTEM, STEM-EDX, ICP, WAXS, EXAFS, Xanes, XPS, NMR...). Surface studies were carried out in some cases, by adsorbing CO on the surface of the particles which was followed by spectroscopic techniques (FT-IR, NMR) to probe their surface state. Some of these nanoparticles were investigated in catalytic reactions, mainly hydrogenation with Rh NPs and hydrogenolysis for RhNiOx NPs. Both colloidal and supported catalytic studies were carried out in the case of hydrogenation catalysis. The originality of this work lies in the development of simple synthesis tools inspired from organometallic chemistry to get well-controlled rhodium-based nanoparticles in terms of size, size distribution, composition and surface state, all these parameters being important whatever the target application. The interest of the obtained nanoparticles in catalysis has been also evidenced in different reactions. This PhD work may open new opportunities of research both in nanochemistry and catalysis.

The aim of this thesis is to investigate the methodology of three dimensional chemical imaging of nanoparticles through the use of scanning transmission electron microscope (STEM) – energy dispersive X-ray (EDX) spectroscopy. In this thesis, an absorption correction factor is derived for spherical nanoparticles that can correct X-ray absorption effects. Quantification of EDX spectra of nanoparticles usually neglects X-ray absorption within the nanoparticle but may lead to erroneous results, thus an absorption correction is important for accurate compositional quantification. The absorption correction presented is verified through comparison with experimental data of Au X-ray peaks in spherical Au nanoparticles and is found to agree excellently. This absorption correction allows accurate compositional quantification of large ( > 100 nm) particles with STEM-EDX.Three dimensional chemical mapping is achievable through the use of EDX spectroscopy with electron tomography. Here, the methodology of STEM-EDX tomography is fully explored, with a focus on how to avoid artefacts introduced through detector shadowing and low counts per pixel. A varied-time acquisition scheme is proposed to correct for detector shadowing that is shown to provide a more constant intensity over a series of projections, allowing a higher fidelity reconstruction. The STEM-EDX tomography methodology presented is applied to the study of AgAu nanoparticles synthesized by the galvanic replacement reaction. The elemental distribution as a function of the composition of the as-synthesized nanoparticles is characterised and a reversal in the element segregated to the surface of the nanoparticles is found. The composition at which the reversal takes place is shown to correlate with a peak in the catalytic yield of a three component coupling reaction. It is hypothesized that a continuous Au surface results in the optimum catalytic conditions for the reaction studied, which guides the use of galvanically prepared AgAu nanoparticles as catalysts.

Doctor of Philosophy / Department of Chemistry / Duy H. Hua / The discovery of new methodologies to advance the fields of synthetic organic, nanoclusters, and polymer chemistry is critical in the asymmetric synthesis of organic compounds. Particularly, catalytic asymmetric oxidation reactions are economic. The oxidation reactions provide chiral molecules and additional functionality onto the molecules for functional group manipulation. New kinds of polymers, namely chiral-substituted poly-N-vinylpyrrolidinones (CSPVPs), stabilize the bimetallic nanoclusters such as Pd/Au or Cu/Au and induce chirality. These chiral polymers wrap around the nanometer-sized (~3 nm) bimetallic nanoclusters and catalyze a number of enantioselective oxidation reactions using oxygen or hydrogen peroxide as the oxidant. Cycloalkanediols were asymmetrically oxidized by 1 atm of oxygen gas to yield the corresponding hydroxyl ketone under the catalysis of Pd/Au (3:1) – CSPVP nanoclusters. Alkenes were oxidized by Pd/Au (3:1)-CSPVP nanoclusters under 2 atmospheric of oxygen in water to give the syn-dihydroxylated products in high chemical and excellent optical yields. Various cycloalkanes underwent regio- and enantio-selective C-H oxidation with Cu/Au (3:1)-CSPVP and 30% hydrogen peroxide to produce the corresponding chiral oxo-molecules in very good to excellent chemical and optical yields. We further discovered an enantioselective desymmetrization of , -dialkenyl-alkanols and , -dialkenyl-amino acid ethyl esters to give chiral disubstituted lactones and lactams, respectively. A number of medium-sized natural products and drugs were also oxidized regioselectively to give the corresponding mono-oxygenated products. A broad-spectrum predictive C-H oxidation of complex molecules is possible. Chapter 1 mainly discussed the synthesis and characterization of the new classes of chiral substituted PVP and bimetallic nanoclusters. Chapter 2 focus on various kind of oxidation reactions by the catalysis of CSPVP stabilized bimetallic nanoclusters. Among various bioluminescence assays, firefly luciferase based bioluminescence assays are popular due to their high specific activity, low background noise and ease of use. However, it has been found that some aromatic carboxylic acid substantially inhibited the firefly luciferase reporter enzyme’s activity. In order to study firefly luciferase inhibition and the proteins associated with inhibition mechanism, we designed two 6-(dimethylamino)-2-phenylisoindolin-1-one derivatives as probe molecules. The synthesis of one probe molecule is discussed in Chapter 3 and the further investigation of its inhibitory activity on firefly luciferase is being conducted by our collaborate.

Well-defined silica supported bimetallic catalysts Pt100-x Pdx (where x is the molar ratio of Pd) are prepared by Surface Organometallic Chemistry (SOMC) via controlled decomposition of Pd2(allyl)2Cl2 on Pt/SiO2. For comparison purposes, Pt100-x Pdx bimetallic catalysts is also prepared by ion-exchange (IE). According to the results of STEM, XAS and H2 chemisorption, all bimetallic nanoparticles, prepared using neither SOMC nor IE, produce discrete formation of monometallic species (either Pt or Pd). Most catalysts exhibit a narrow particle size distribution with an average diameter ranging from 1 to 3 nm for samples prepared by IE and from 2 to 5 nm for the ones synthesized by SOMC. For all catalysts investigated in the present work, iso-butane reaction with hydrogen under differential conditions (conversions below 5%) leads to the formation of methane and propane (hydrogenolysis), n-butane (isomerization), and traces of iso-butylene (dehydrogenation). The total rate of reaction decreases with increasing the Pd loading for both catalysts series as a result of decreasing turnover rate (expressed as moles converted per total surface metal per second) of both isomerization and hydrogenolysis. In the case of Pt100-x Pdx(SOMC) catalysts, the results suggest a selective coverage of Pt (100) surface by a Pd layer, followed by a buildup of Pd overcoat onto a Pd layer assuming that each metal keeps its intrinsic catalytic properties. There is no mutual electronic charge transfer between the two metals (DFT). For the PtPd catalysts prepared by IE, the catalytic behavior cannot simply be explained by a surface coverage of highly active Pt metal by less active Pd (not observed), suggesting there is formation of a surface alloy between Pt and Pd collaborated by EXAFS and DFT. The catalytic results are explained by a simple structure activity relationship based on the previously proposed mechanism of C-H bond and C-C Bond activation and cleavage for iso-butane hydrogenolysis, isomerization, cracking and dehydrogenation.

Copper-based materials are one of the most promising catalysts for performing transformations of important organic compounds in both academic and industrial operations. However, it is challenging to consistently synthesize highly active and stable copper species as heterogeneous catalysts due to their relatively high surface energy. As a result, agglomeration usually occurs, which limits the catalytic activities of the copper species. The work presented in this dissertation shows different synthetic strategies for obtaining active and stable copper-based materials by modifying chemical/physical properties of copper nanoparticles (NPs). Emphasis is placed on discussing specific catalytic systems, including carbon-supported catalysts (monometallic and bimetallic copper-based heterogeneous catalysts) and titania-supported catalysts, and their advantages in terms of catalytic performance. In recent years, there has been increasing interest in using metal-organic frameworks (MOFs) as a sacrificial template to obtain carbon-supported NPs via a thermolysis process. The advantages of using MOFs to prepare carbon supported nanomaterials are a fine distribution of active particles on carbon matrix without post-synthesis treatments and corresponding increased catalytic activity and stability in many reaction conditions. To better understand the potential of this synthetic approach, MOF pyrolyzed products have been characterized. Then, they were applied as heterogeneous catalysts for several chemical reactions. In particular, the high energy copper-based MOF, CuNbO-1, was decomposed to obtain an amorphous copper species supported on carbon (a-Cu@C). This catalyst was found to be highly active for reduction, oxidation, and N-arylation reactions without further tuning or optimization. Higher catalyst turnover numbers for each of these transformations were obtained when comparing a-Cu@C activity to that of similar Cu-based materials. To improve catalyst performance, a secondary metal can be introduced to create synergistic effects with the parent copper species. In order to gain insights into the role of the second metal, a well-known Cu-MOF, HKUST-1, was doped with nickel, cobalt, and silver solutions, followed by a decomposition process with 2,4,6-trinitrotoluene (TNT) as additive. This additive was used to enhance the rapid thermolysis of the bimetallic MOFs. In these bimetallic systems, the addition of a second metal was found to help in dispersing both metals over the carbon composite support and in influencing the particle size and oxidation state of the metals. Catalytic performance showed that even <1% of a secondary metal increased the rate for nitrophenol reduction. Optimal catalytic performance was achieved using a Ni-CuO@C bimetallic catalyst. Another synthetic strategy for Cu-catalyst preparation involves using the deposition-precipitation method, in which a copper catalyst anchored on a titania support was synthesized at low weight % in order to obtain a single atom catalyst (1-Cu/TiO2). The higher copper loading catalyst, 5-Cu/TiO2, was synthesized as a benchmark catalyst for comparison. The copper structure in the synthesized catalysts was investigated by powder X-ray diffraction (PXRD), Raman, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX), X-ray photoelectron spectroscopy (XPS), N2 physisorption and inductively coupled plasma mass spectrometry (ICP-MS) in order to characterize physical and chemical properties. STEM-EDX observations showed single atom copper species less than 0.75 nm in size, as well as nanoparticles with an average diameter of ~1.31 nm. This catalyst was highly active in the reduction of nitro-aromatic compounds with NaBH4 at room temperature. The small to atomic level sizes of the Cu species and multiple oxidation states of Ti species were found to play a crucial role in the catalytic activity.

The Diesel Oxidation Catalyst (DOC) is subjected to harsh conditions, causing its performance to diminish over time as the result of different aging mechanisms, which either decreases or lowers the accessibility to the catalyst’s active sites. Previous work using chemisorption to quantify aging progression has resulted in a reproducibility of 17%. In this study it has been attempted to lower this, while also performing performance evaluations to see if correlations exist between dispersion and Light-Off Temperature (LOT). Two catalysts have been investigated, LLC (Low Loading Catalyst) and HLC (High Loading Catalyst). These were hydrothermally aged at 600 C, 700 C and 800 C. In addition to these, two HLC engine cell samples were also investigated. To ensure sample homogeneity, different sample preparation methods were investigated. Catalyst samples were crushed, or had their washcoat layer removed, or were milled and then sieved. A total of 5 runs were done using fresh catalysts of LLC and HLC to calculate the standard deviation. Evaluation of performance was done on all samples using Synthetic Catalyst Activity Testing (SCAT). It was deemed that the only viable sample preparation method was to mill and sieve as other methods would be hard to reproduce. The results showed that the reproducibility for LLC was %STD = 4% and for HLC %STD = 2%. For LLC, a correlation between catalytic activity and dispersion was found. The activity dropped with respect to the dispersion in a close to linear fashion without a large effect on BET surface area. For HLC the dispersion decreased largely upon hydrothermal aging, however no correlation was found with the activity; only when aged at 800 C a significant change in LOT was noted. The BET surface area measurements were inconsistent. Lower dispersion sometimes resulted in higher surface area. Engine cell samples exhibited notable decrease in dispersion, but not in surface area, and did not correlate to the hydrothermally aged catalysts, which might be due to other effects inhibiting CO chemisorption during measurements. / Dieseloxidationskatalysatorn (DOC) utsätts för tuffa förhållanden, vilket medför att dess prestanda minskar med tiden på grund av olika åldringsmekanismer, vilka antingen minskar dess aktiva säten eller minskar tillgängligheten till dessa. Tidigare studier då kemisorption använts för att kvantifiera vilken utsträckning katalysatorn har blivit deaktiverad har resulterat i en reproducerbarhet på 17%. Denna studie har syftat till att minska detta, men även till att utföra prestandamätningar för att se om det existerar korrelationer mellan dispersion och tändtemperatur (LOT). Två katalysatorer undersöktes, LLC (lågladdad katalysator) och HLC (högladdad katalysator), både som färska, men även som hydrotermiskt åldrade i 600 C, 700 C and 800 C. Dessutom undersöktes två motorcellsprover av HLC. För att säkerställa provhomogenitet undersöktes olika provprepareringsmetoder. Katalysatorprover krossades, eller fick washcoat avlägsnat eller maldes samt siktades. Totalt fem körningar gjordes på färska katalysatorer (LLC och HLC). Prestandamätningar gjordes på samtliga prov i Synthetic Catalyst Activity Testing (SCAT). Det bedömdes att den enda gångbara provprepareringsmetoden var att mala samt sikta katalysatorn då de andra metoderna skulle bli svåra att upprepa på ett reproducerbart sätt. Resultaten visade att reproducerbarheten för LLC var %STD = 4% och för HLC %STD = 2%. LLC visade på korrelation mellan katalytisk aktivitet och dispersion. Aktiviteten minskade linjärt utan större förluster i BETytarea. För HLC minskade dispersionen i hög grad med ökad åldringstemperatur, däremot kunde ingen korrelation med katalytisk aktivitet påvisas; enbart då katalysatorn åldrades vid 800 C ändrades LOT signifikant. Förändringarna i BET-ytarean var inte beroende av åldringstemperatur då lägre dispersion ibland resulterade i högre ytarea. För motorcellsproverna uppmättes en märkbart låg dispersion, medan ytarean var relativt oförändrad. Dessa resultat kunde inte korreleras till de hydrotermiskt åldrade proverna, vilket kan bero på att andra effekter inhiberat CO kemisorptionen.

Bimetallic Catalysis is an emerging field of study that uses two metals to cooperatively perform organic transformations. These metals can serve to activate or bind substrates in order to increase the rate and selectivity of reactions. This work first describes the synthesis and utilization of six new chiral, titanium-containing phosphinoamide ligands. These Lewis acidic ligands withdraw electron density from an active palladium center to induce chirality and increase the rate of allylic amination of hindered, secondary N-alkyl amines. X-ray quality crystals were grown for each ligand and completed the allylic amination of hindered secondary amines in minutes whereas other non-titanium-containing ligands produced trace product. Although enantioselectivity was low initially, through a dynamic kinetic resolution enantioselectivity was increased over time, reaching 53% enantioselectivity. The second type of bimetallic catalysis discussed is dinuclear Pd(II) and Pd(I) catalysis. These dimers were built on a 2-phosphinoamide ligand scaffold and present interesting molecular structure and unique reactivity. These dimers were found to perform tandem arylketone coupling to produce disubstituted naphthalene products under oxidative conditions. It is proposed that the Pd(II) dimer undergoes oxidative addition to produce a Pd(III) dimer which subsequently produces an aryl-ketone intermediate. This process is made possible by the cooperativity of the two palladium centers which enable the formation of a Pd(III) dimer, circumventing the need for the high energy Pd(IV) oxidation state. Oxidative conditions then allows coupling and cyclization of a second ketone to form the naphthalene product.

No description available.

A thermo-mechanical finite element model is developed to determine the temperature history and residual stresses in a Cu-H13 thin-walled plate deposited by the Laser Engineered Net Shaping (LENSTM) process. The same model is also applied to a H13-H13 sample to compare the results. The input laser power is adjusted to maintain a steady molten pool size and depth. For a constant scanning speed the laser power decreases with the addition of more layers, and with the increase of scanning speed the laser power needs to be increased. The Z-component of residual stresses is greater than the other components, and is compressive near the center of the wall and tensile at the free edges. The residual stress levels near the free edges are higher in the H13-H13 sample than in the Cu-H13 sample. In these regions, the use of unidirectional scanning results in a higher stress accumulation than the alternating scanning.