The research in this dissertation examines the chemistry and applications of dendrimers in homogeneous catalysis. We examined interactions between dendrimers and charged probe molecules, prepared dendrimer-encapsulated metal nanoparticles in organic solvents, studied size-selectivity of dendrimer-encapsulted catalysts, and designed molecular rulers as in-situ probes to measure the location of dendrimer-encapsulted metal nanoparticles. The intrinsic proton binding constant and a constant that characterizes the strength of electrostatic interactions among occupied binding sites in poly(amidoamine) (PAMAM) dendrimers have been obtained by studying the effect of solution pH on the protonation of the dendrimers. The significant finding is that these two factors are greatly modulated by the unique and hydrophobic microenvironment in the dendrimer interior. Hydrophilic poly(propylene imine) (PPI) dendrimers were modified with various hydrophobic alkyl chains through an amide linkage and were then used as templates for preparing intradendrimer copper nanoclusters. The main driving force for encapsulating metal-ions was found to be the differences in metal-ion solubility between the solvent and the interior of the dendrimer. Nanometer-sized metal particles are synthesized and encapsulated into the interior of dendrimers by first mixing together the dendrimer and metal ion solution and then reducing the composite chemically, and the resulting dendrimer-encapsulated metal nanoparticles can then be used as catalysts. By controlling the packing density on the dendrimer periphery using either different dendrimer generations or dendrimer surface functionalities, it is possible to control access of substrates to the encapsulated catalytic nanoparticle. Molecular rulers consisting of a large molecular "stopper", a reactive probe and a linker were designed as in-situ probes for determining the average distance between the surface of dendrimer-encapsulated palladium nanoparticles and the periphery of their fourth-generation, hydroxyl-terminated PAMAM dendrimer hosts. By doing so, we avoid having to make assumptions about the nanoparticle size and shape. The results suggest that the surface of the encapsulated nanoparticle is situated 0.7 ± 0.2 nm from the surface of the dendrimer.

La catàlisi asimètrica es part de la síntesi asimètrica i fa possible la transformació de substrats pro-quirals o racèmics en productes quirals emprant quantitats catalítiques de compostos que contenen informació quiral. El disseny de nous lligands es l'etapa clau per a obtenir alts nivells de reactivitat i selectivitat. Els carbohidrats son uns dels membres més importants dintre de la "chiral pool".Aquesta tesi esta enfocada en el desenvolupament i aplicació en catàlisi asimètrica de nous lligands amb esquelet carbohidrat.Aquestos lligands foren aplicats amb èxit a la hidroformilació asimètrica catalitzada per Rh d'alquens monosubstituïts, interns disubstituïts i 1,1´-disubstituïts.L'efecte de les modificacions estructurals dels lligands 1,3-difosfit sobre els resultats catalítics a l'alquilació al·lílica catalitzada per Pd de compostos fenil-al·lílics ha sigut també estudiat en aquesta tesis. Finalment, els lligands 1,3-difosfit han sigut aplicats a l'estabilització de nanopartícules metàl·liques, i la seva aplicació a la hidrogenació de o- i m-metilanisol. / Asymmetric catalysis is part of the asymmetric synthesis and makes possible the transformation of a pro-chiral or racemic substrate into a chiral product using catalytic amounts of the compounds which contain the chiral information. The design of new ligands is perhaps the most crucial step to achieve the highest levels of reactivity and selectivity. Carbohydrates are the most prominent members of the "chiral pool".This thesis focus on the development and application in asymmetric catalysis of new 1,3-diphosphite with carbohydrate backbone. These ligands were successful applied in the Rh-asymmetric hydroformylation of monosubstituted, disubstituted internal and 1,1´-disubstituted alkenes.The effect of the structural modification of these 1,3-diphosphite ligands on the catalytic results of the Pd-allylic alkylation of phenyl-allyl compounds was also studied in this thesis. Finally, the 1,3-diphosphites ligands were applied to stabilize metal nanoparticles. These nanocatalysts were tested in the hydrogenation of pro-chiral o- and m-methylanisole.

Project I: [Ru(OH2)3(4'-phenyl-2,2':6',2''-terpyridine)](OTf)2 as a Homogeneous Hydrogenation Catalyst for Biomass Derived Substrates. The complex [Ru(OH2)3(4'-phenyl-2,2':6',2''-terpyridine)](OTf)2 has been shown to be an active ionic hydrogenation catalyst for selected carbonyls, diols and glycerol by the Schlaf group. It was postulated to also be active for other biomass derived substrates such as levulinic acid (LA), furfural and 5-hydroxymethyl furfural (HMF). Synthesis of the complex was optimized and full characterization carried out by 1H/13C –NMR. The complex was tested against LA in aqueous sulfolane medium and the furfural/HMF model system 2,5-hexanedione in water. Activity of the complex was compared to the analogous metal-ligand bifunctional (MLB) system described in Project II. The complex exhibited good thermal stability up to 200 oC in 90/10 wt% sulfolane/water mixtures and was capable of hydrogenation of LA to γ-valerolactone in 95% yield. Addition of protic acids to the reaction mixture and increasing proportions of water decreased the activity of the complex towards the hydrogenation of LA. Project II: [Ru(OH2)3(di(picolyl)amine)](OTf)2 as an acid-, water- stable, metal-ligand bifunctional deoxygenation catalyst. The complex [Ru(OH2)3(di(picolyl)amine)](OTf)2 was postulated to be an active MLB ionic hydrogenation catalyst under acidic aqueous conditions. Using the substantially labile [Ru(DMF)6](OTF)3 ruthenium complex as the precursor, the desired complex was prepared insitu by coordination of the DPA ligand and concomitant reduction of Ru3+ to Ru2+. The complex was characterized by 1H/13C-NMR and tested for the hydrogenation of LA, 2,5-hexanedione, furfural and HMF under acidic aqueous conditions. The complex exhibited thermal stability up to 150 oC and was active for the hydrogenation of carbonyls, as demonstrated by the conversion of 2,5-hexanedione to 2,5-hexanediol in 94% yield in water. Addition of H3PO4 as an acid cocatalyst resulted in nearly complete conversion to dimethyltetrahydrofuran (DMTHF) but further deoxygenation could not be achieved. Direct comparision of [Ru(OH2)3(di(picolyl)amine)](OTf)2 and [Ru(OH2)3(4'-phenyl-2,2':6',2''-terpyridine)](OTf)2 under identical conditions against LA and 2,5-hexanedione demonstrated that the[Ru(OH2)3(di(picolyl)amine)](OTf)2 catalyst is more active than the [Ru(OH2)3(4'-phenyl-2,2':6',2''-terpyridine)](OTf)2 complex in all cases, suggesting that the di(picolyl)amine complex operates through a MLB ionic hydrogenation mechanism. / NSERC

Abstract: A brief overview of this PhD thesis, The emergence of nanotechnology has stimulated both fundamental and industrially relevant studies of the catalytic activity of noble metal nanoparticles. Palladium, ruthenium and gold are well known catalysts when used in nanoparticle- based systems. This body of work endeavoured to investigate the catalytic activity of these noble metal nanoparticles through three studies as a briefly overviewed below. Study 1: Palladium is a well-known catalyst, even in bulk phases, but its high cost had driven industry towards its use in nanoparticle- based systems well before nanotechnology had attracted the attention of the media. Palladium nanoparticles often show remarkable catalytic activity and selectivity, particularly for the hydrogenation of some unsaturated hydrocarbons, such as alkenes, alkynes and unsaturated carbonyl compounds. The nature of supports can affect the catalytic activity and selectivity of metal-support interaction. Natural polymeric supports, such as wool, can be suitable for new generation of composite materials incorporating nanosized metal nanoparticles and have the added advantage of being “environmentally friendly”. Catalytic hydrogenation of cyclohexene to cyclohexane by palladium nanoparticles immobilized on wool was demonstrated by using a Parr high pressure hydrogenation set-up. The efficiency of the process was explored over loading rates from 1.6% to 2.6% of palladium nanoparticles (by weight) with a variety of particle sizes. Optimization of the reaction conditions including, stirring rate, amounts of reactants, gas pressure and target temperature, led to series of catalytic activity tests carried out for 5 or 24 hours (each) at 400psi H2 and 40 oC using a stirring rate 750 rpm. Product mixtures were analysed using gas chromatography (GC-FID) to determine conversions. Samples S1 and S2 proved to be the most active catalysts because the average Pd particle size was around ~5 nm and the particles were more accessible for the reactant (i.e., Pd particles were on the surface of wool). However, under the catalytic testing conditions studied, wool (Pd/wool) did not show advantages over commercially used palladium nanoparticles on activated carbon (Pd/C). Study 2: Ruthenium fabricated as noble metal nanoparticles can be catalytically active for hydrogenation of organic compounds. However, a challenging issue for researchers is that Ru nanocatalysts can be spontaneously deactivated due to effects, such as sintering or leaching of active components, oxidation of noble metal nanoparticles, inactive metal or metal oxide deposition and impurities in solvents and reagents. Calcination of noble metal nanoparticles is one option for reactivation of Ru nanoparticles immobilized on SiO2 (Ru/SiO2) utilized as nanocatalysts in chemical reactions. In fact, the catalytic activity of noble metal nanoparticles is known to be proportional to the active part of the surface area. The effects of calcinations on catalytic activity of “shape- specific” 0.1 wt% Ru/SiO2 for hydrogenation of cyclohexene to cyclohexane were investigated. Optimization of calcinations by varying temperature and time proved to be effective on the activity of nanocatalysts retaining the Ru nanocatalysts shapes for the hydrogenation of cyclohexene. Product mixtures were analysed using gas chromatography (GC-FID) to determine conversions. The Ru catalysts showed the highest activity (100%) when they were activated by calcination following protocol No.1 in a furnace under the mildest reductive conditions studied (temperature = 200 oC for 1 hour, which was the shortest calcination time). HRTEM study showed only minor deformation of the Ru nanoparticles and minimal aggregation for this type of activation. Study 3: Supported gold nanoparticles have excited much interest owing to their unusual and somewhat unexpected catalytic activity particularly with the selective oxidation of organic compounds. Gold nanoparticles immobilized on Norit activated carbon (Au101/C) via colloidal deposition gave high selectivity of benzyl alcohol oxidation. The presence of a base (K2CO3) increased the catalytic activity of gold nanocatalysts (which was negligible in the absence of base) through dehydrogenation of the alcohol via deprotonation of a primary OH groups, and helped overcome the rate-limitation step of the oxidation process. The interaction between the gold species and the support was investigated by measuring change in catalytic activity with different activation methods (i.e., washing with a solvent at elevated temperature, and/or followed by calcinations). A mixture of benzyl alcohol as a reactant, methanol as a solvent, K2CO3 as a base and oxygen gas was studied by the activated gold nanocatalysts using a mini reactor set-up. The efficiency of the process was explored by varying the amounts of benzyl alcohol and the base, target temperature, metal loading of the gold catalysts rate and the solvent, between 3 and 24 hours at 73 psi O2 and a stirring rate (750 rpm). The samples of the reaction mixture were centrifuged and analysed by highperformance liquid chromatography (HPLC) to determine conversions. The effect of size on the catalytic activity was studied for different types of gold particles (Au101, Aunaked and Aucitrate) and clusters (Au8 and Au9) immobilized on powder Norit activated carbon. The highest activity of benzyl alcohol oxidation was observed for activated 1.0 wt% Au101/C catalysts (washed with toluene and followed by calcination under vacuum at 100 oC for 3 h) for ~3.5 nm gold particles. Additionally, the support effect was studied for gold particles immobilized on different types of carbons, such as Norit activated carbon (powder, granular and powdered) and mesoporous carbons (CMK-3, CMK-8 and NCCR-41), granular modified carbon (–SH and –SO3H groups) and Vulcan carbon. The highest activity was observed by activated 1.0 wt% Au101/C8 catalysts (washed with toluene and followed by calcination under vacuum at 100 oC for 3 h). Activated 1% Au101/C41 (washed with toluene followed by calcination under vacuum at 100 oC for 3 hours) with 2.6 ± 0.1 nm gold particle size showed the highest selectivity towards methyl benzoate as a main product (S%: 88%) after 3 hours reaction time. However, activated 1% Au101/C (calcination in O2 -H2 at 100 oC for 3 hours) with 6.6 ± 0.3 nm gold particle size exhibited the highest selectivity towards benzoic acid as a main product (S: 86%) after 24 hours reaction time.Therefore, particle size and type of carbon support can be considered as playing crucial roles in defining the catalytic activity of gold nanocatalysts which were used for benzyl alcohol oxidation.

The catalytic activity of ruthenium(II) bis(diimine) complexes cis-[Ru(6,6′-Cl2bpy)2(OH2)2](Z)2 (2, Z = CF3SO3; 3, Z = (3,5-(CF3)2C6H3)4B ,i.e. BArF), cis-[Ru(4,4′-Cl2bpy)2(OH2)2](Z)2 (4, Z = CF3SO3; 5, Z = BArF) and cis-[Ru(bpy)2(PR3)(OH2)](CF3SO3)2 (7, bpy = 2,2’-bipyridine, PR3 = P(C6H4F)3; 8, bpy = 2,2-bipyridine, PR3 = PPh3; 9, bpy = 4,4’-dichloro-2,2’-bipyridine, PR3 = PPh3; 10, bpy = 4,4’-dimethyl-2,2’-bipyridine, PR3 = P(C6H4F)3) for the hydrogenation and hydrogenolysis of furfural (FFR), furfuryl alcohol (FFA) and 5-hydroxymethylfurfural (HMF) was investigated. The compounds 2-5 are active and highly selective catalysts for the hydrogenation of FFR to FFA. Using 2 as catalyst at 100 °C, hydrogenation of FFR proceeded to high conversion (≥98%) and with 100% selectivity to FFA in 2 h. The catalyst cis-[Ru(6,6′-Cl2bpy)2(OH2)2](CF3SO3)2 (2) also showed some activity for hydrogenolysis of FFR and FFA at 130 °C in ethanol, giving up to 25% of 2-methylfuran (MF) yield. The catalyst 3 alsodisplayed high catalytic activity for the hydrogenation of FFA to tetrahydrofurfuryl alcohol. Catalysts 7-10 are also active towards the hydrogenation of furfural (FFR) in NMP giving >90% FFR conversion with 100% selectivity for furfuryl alcohol (FFA) in 12 h. Compounds 7-10 are active C-O bond hydrogenolysis catalysts in presence of bismuth halide Lewis acids. For example, hydrogenolysis of FFA in the presence of 1 mol% of catalyst cis-[Ru(4,4’-Cl2bpy)2(PPh3)(OH2)](CF3SO3)2 (9) and 20 mol% bismuth bromide at 180 °C/51 atm H2 pressure gave >96% conversion of FFA and 55% MF yield. Compounds 7-10 in the presence of bismuth halides, showed almost 100% conversion of HMF with a very high selectivity (65-72%) for 2,5-DMF, along with 10-12% of MF, and trace amount of 5-methylfurfural (MeFFR). In order to test the activity of ruthenium hydrides towards the C-O bond hydrogenation and hydrogenolysis of HMF, series of monocationic ruthenium complexes cis-[Ru(bpy)2(PR3)(H)](CF3SO3) (12, bpy = 2,2’-bipyridine, PR3 = P(C6H4F)3; 13, bpy = 2,2-bipyridine, PR3= PPh3; 14, bpy = 4,4’-dimethyl-2,2’-bipyridine, PR3= P(C6H4F)3) were prepared. The hydrogenation of HMF using catalysts 12-14, produced 70-72% of 2,5-DMF and 11% MF, suggesting that ruthenium hydrides are active and efficient catalysts for HMF hydrogenation.

Electrospray ionization mass spectrometry (ESI-MS) has been applied to the realtime study of homogeneous organometallic reactions. ESI-MS as a soft ionization technique is amenable to fragile organometallic complexes, and as a fast and sensitive technique is ideal for detecting low concentration intermediates within reactions. Pressurized sample infusion (PSI) was used for continuous sample infusion into the mass spectrometer, granting the air-free conditions necessary for these reactions to be successful, and resulting in reaction profile data that contains information about the dynamics of speciation of the catalyst. Collision induced dissociation (CID) was used to probe the binding affinities of various bisphosphine ligands as well as in characterizing intermediates in reactions. PSI ESI-MS was applied to the hydroboration reaction of the alkene tert-butylethene using the amine-borane H3B⋅NMe3 catalyzed by [Rh(xantphos)]+ fragments to show how the reaction progresses from substrates to products. PSI ESI-MS was also applied to the hydrogenation of a charge-tagged alkyne [Ph3P(CH2)4C2H]+[PF6]-, catalyzed by a cationic rhodium complex [Rh(PcPr3)2(η6-FPh)]+[B{3,5-(CF3)2C6H3}4]– (PcPr3 = triscyclopropylphosphine, FPh = fluorobenzene). This work demonstrated the use of ESI-MS in conjunction with NMR, kinetic isotope effects and numerical modeling for determining a mechanism of reaction. The hydroacylation reaction of a β–S substituted aldehyde and an alkyne catalyzed by [Rh(PiPr2NMePiPr2)(η6-FPh)]+[B{3,5-(CF3)2C6H3}4]– (PiPr2 = diisopropylphosphine) was studied by PSI ESI-MS while employing charged tags, allowing for observation of reaction progress and some key intermediates. A new concept for mechanistic analysis has been developed: coupling of an orthogonal spectroscopic technique with PSI ESI-MS. This new method was applied to the same hydroacylation reaction studied with charged tags. The use of IR in conjunction with ESI-MS led to rate information about the overall reaction along with dynamic information about catalytic speciation. Coupling of these techniques allows for detection over many magnitudes of concentration. / Graduate

Ethylene hydrogenation on Ni(111) / equilibrium geometry calculations for Ni2 dimer, Ni13 and Ni55 nanoclusters / and ethylene adsorption on Ni(100), Ni(111), Ni2, and Ni13 were studied quantum mechanically by means of energetic and kinetic differences. Ethylene hydrogenation on Ni(111) was simulated by use of DFT/B3LYP/6-31G** formalism. The reaction mechanism was mainly composed of three elementary steps. Firstly, ethylene adsorption on bare Ni(111) surface was performed. Second step and third step were the formation of ethane from adsorbed ethylene by use of two types of hydrogen atom, bulk and surface. During the hydrogenation reaction of ethylene on Ni(111), bulk hydrogen atom, representing for hydrogen atoms emerging from the bulk of Ni metal, was determined to be rather reactive than surface hydrogen atom, as suggested by experimental findings. Small Ni clusters, Ni2 and Ni13, were investigated by means of DFT/B3LYP/modified-6-31G**. Equilibrium geometry calculations resulted in Ni2 binding energy of 1.078eV/atom, showing good agreement with experimental value. Ni13 was found to have a structure of icosahedral, suggested experimentally, and binding energy of 2.70eV/atom. Ni55 was, also, studied by semi-empirical PM3 formalism, resulting in expected icosahedral structure. Finally, DFT/B3LYP/6-31G** investigation of ethylene adsorption was performed on Ni(111), Ni(100) and Ni13 surfaces which were selected according to their nickel atom coordination numbers of 9, 8 and 6, respectively. Comparison of adsorption energies of -18.00kcal/mol, -31.4kcal/mol and -43.42kcal/mol, respectively, indicated that the change in energies for ethylene adsorption on different nickel surfaces was directly proportional to coordination number of the nickel atoms constructing the surfaces.

In polycrystalline silicon (pc-Si) thin-film solar cells, defect passivation is critical to device performance. Isoelectronic or covalently bonded impurities, hydrogenic, extended defects and defects with localized levels in the bandgap (deep level defects) are typically introduced during the fabrication of, and/or are inherent to, pc-Si thin-film solar cells. These defects dramatically affect minority carrier lifetimes. Removing and/or passivating these defects is required to maximize minority carrier lifetimes and is typically done through thermal annealing and passivation techniques. For pc-Si thin-film solar cells on low temperature glass superstrates, rapid thermal annealing (RTA) and hydrogen plasma passivation (hydrogenation) are powerful techniques to achieve effective removal and passivation of these defects. In this thesis, three silicon thin-film solar cells structures on low-temperature glass are subjected to variations in RTA high-temperature plateaus, RTA plateau times, and hydrogen plasma passivation parameters. These solar cells are referred to as ALICIA, EVA and PLASMA. By varying the RTA plateau temperature and time at plateau, the trade-off between extensive dopant diffusion and maximum defect removal is optimized. To reduce the density of point defects and to electrically activate the majority of dopants, an RTA process is shown to be essential. For all three of the thin-film solar cell structures investigated in this thesis, a shorter, higher-temperature RTA process provides the best open-circuit voltage (Voc). Extensive RTA plateau times cause excessive dopant smearing, increasing n = 2 recombination and shunt resistance losses. Hydrogenation is shown to be an essential step to achieve maximum device performance by `healing' the defects inherent to pc-Si thin-film solar cells. If the hydrogen concentration is about 1-2 times the density of oxygen in the cells as measured by secondary ion mass spectroscopy (SIMS), the cells seem to respond best to hydrogenation, with good resultant Voc and short-circuit for all cells investigated in this thesis. The effect of hydrogen passivation on the Voc is spectacular, typically increasing it by a factor of 2 to 3.5. Hydrogen de-bonding from repeated thermal treatments at increasing temperature provides a deeper understanding of what defects exist and the nature of the defects that limit the cell voltage. The variation in RTA and hydrogenation process parameters produces significant empirical insight into the effectiveness of RTA processes for point defect removal, dopant activation, point defect and grain boundary passivation, and impurity passivation. SIMS measurements are used to determine the impurities present in the cells' bulk and the amount of hydrogen available to passivate defects. From the results presented it appears that pc-Si thin-film solar cells on low-temperature glass are a promising, and potentially lower-cost, alternative to Si wafer based cells.

One of the poly-Si thin-film cells developed at the University of New South Wales (UNSW) is the EVA cell. In this work, SiN films for EVA cells as an antireflection/barrier coating were investigated. In addition, the effect of hydrogenation pre-treatment of solid phase crystallisation (SPC) on grain size and open-circuit voltage (Voc) was investigated. The SiN films deposited by PECVD were examined for uniformity of the thickness and the refractive index of the films across the position of the samples in the PECVD deposition system. A spectrophotometric analysis was used to determine these film properties. It was found that these properties were very uniform over the deposition area. Good repeatability of the depositions was also observed. A series of SiN film depositions by reactive sputtering were also performed to optimize the deposition process. Parameters adjusted during the deposition were nitrogen flow rate, substrate bias, and substrate temperature. By investigating the deposition rate, refractive index, and surface roughness of the films, the three deposition parameters were optimised. The effects of post SiN deposition treatments (a-Si deposition, SPC, RTA, and hydrogenation) on thickness and refractive index of both SiN films deposited by PECVD and reactive sputtering were investigated by using samples which have the same structure as the EVA cells. The thickness of the PECVD SiN films decreased about 6 % after all the treatments. On the other hand, the thickness reductions of the reactively sputtered SiN films were very small. The refractive index of the PECVD SiN films increased about 0.6 % after the treatments, whereas that of the reactively sputtered SiN films decreased 1.3 % after the treatments. As a possible method to improve the performance of EVA cells, hydrogenation of a-Si was investigated as a pre-treatment of SPC process. There were no obvious differences in the grainsize and the Voc of the EVA cells with and without the hydrogenation. Therefore it is likely that the hydrogenation pre-treatment of SPC does not have a beneficial effect on the performance of EVA cells.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.