The research in this thesis involves the synthesis and characterization of nanoparticle catalysts for oxidation reactions. It includes two projects: 1) polymer-stabilized Au, Pd and bimetallic AuPd nanoparticle catalysts for alcohol oxidation reactions, and 2) oxidative stabilities and catalytic activities of thiolate- and dithiolate-protected Au monolayer-protected clusters (MPCs).<p>n the first project, alcohol oxidations under mild conditions using polyvinylpyrrolidone (PVP)-stabilized Au, Pd and bimetallic AuPd nanoparticle catalysts in aqueous solutions have been investigated. The catalytic activities of the nanoparticles towards the oxidation of benzyl alcohol, 1-butanol, 2-butanol, 2-buten-1-ol and 1,4-butanediol indicate that bimetallic 1:3 Au:Pd nanoparticles have higher catalytic activities than Au, Pd and other bimetallic AuPd nanoparticles, and that selectivities towards specific products can often be tuned using bimetallic particles. In addition, advantages and disadvantages for the use of such nanoparticle catalysts as mild, environmentally-friendly oxidation catalysts have been examined. This work has recently been published in the Journal of Catalysis.<p>In the second project, 1-dodecanethiolate-, dithiolate-, and 1:1 mixed 1-dodecanethiolate/dithiolate-protected Au MPCs have been synthesized and their thermal stability, oxidative stability in the presence of oxygen and cyanide anions have been studied. These systematic investigations reveal the stability of Au MPCs can be tuned by choosing different thiolate ligands and oxidation conditions. Partially-oxidized thiolate-protected Au MPCs which have substrate-accessible surfaces and are stabilized by residual thiolate ligands show indications they will be promising catalysts. The catalytic activities of 1-dodecanethiolate-, dithiolate-, and 1:1 mixed 1-dodecanethiolate/dithiolate-protected Au MPCs for catalytic 4-nitrophenol reduction with sodium borohydride were investigated, and all the Au MPCs showed high catalytic activity for this reaction.

This work began with the synthesis and full characterization of a novel £^-diimine ligand, (2,6-iPr2C6H3N=CH)2C6H4, from the reaction of o-phthaladehyde and the bulky aniline, 2,6-diisopropylaniline. It was observed that any <i>di-ortho</i>-substituted aniline with less bulky groups than isopropyl groups resulted in formation of the corresponding iminisoindolines. Reaction of the £^-diimine ligand with PdCl2 did not result in a seven-membered coordination complex, but in non-palladacyclic complex, [(g-diimine)PdCl(Ý-Cl)]2. Whereas reaction with Pd(OAc)2 gave an S-shaped five-membered trinuclear palladacyclic complex, {1,2-(2,6-iPr2-C6H3N=CH)2-C6H3]Pd(Ý-OAc)2}2Pd. These complexes were found to be active precatalysts for Heck and Suzuki coupling reaction giving TONs of up to 104 and 86, for arylbromides and arylchlorides, respectively.<p> On the other hand, a series of neutral and cationic seven-membered aluminum coordination complexes were obtained from the reaction of £^-diimine with a variety of aluminum species (AlMe3, AlMe2Cl, AlMeCl2 and AlCl3). The synthesis and characterization of these complexes are exemplified.<p> Also illustrated in this thesis is the synthesis and characterization of a series of air- and moisture-stable iminoisoindoline-based palladacyclic compounds of the general formula, [(iminoisoindoline)Pd{Ý-OAc}]2. These six-membered palladacyclic complexes were obtained through a simple two-step protocol as analytically pure solids. Phosphine-ligated mononuclear palladacycles of the general formula, [Pd(iminoisoindoline)X(PR3)], X= OAc or Cl, R = Ph or Cy, are also described. Dinuclear palladacycles were also found to be active for the Heck and Suzuki C-C coupling reactions. TONs of up to 106, 105 and 60 were observed for coupling of iodobenzene, <i>p</i>-acetylbromobenzene and <i>p</i>-chlorobenzaldehyde, respectively in the Heck coupling reaction.

This research is focused on development of routes towards the rational design of nanoparticle catalysts. Primarily, it is focused on two main projects; (1) the use of imidazolium-based ionic liquids (ILs) as greener media for the design of quasi-homogeneous nanoparticle catalysts and (2) the rational design of heterogeneous-supported nanoparticle catalysts from structured nanoparticle precursors. Each project has different studies associated with the main objective of the design of nanoparticle catalysts.<p> In the first project, imidazolium-based ionic liquids have been used for the synthesis of nanoparticle catalysts. In particular, studies on recyclability, reuse, mode-of-stability, and long-term stability of these ionic-liquid supported nanoparticle catalysts have been done; all of which are important factors in determining the overall greenness of such synthetic routes. Three papers have been published/submitted for this project. In the first publication, highly stable polymer-stabilized Au, Pd and bimetallic Au-Pd nanoparticle catalysts have been synthesized in imidazolium-based 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) ionic liquid (Journal of Molecular Catalysis A: Chemical, 2008, 286, 114). The resulting nanoparticles were found to be effective and selective quasi-homogeneous catalysts towards a wide-range of hydrogenation reactions and the catalyst solution was reused for further catalytic reactions with minimal loss in activity. The synthesis of very pure and clean ILs has allowed a platform to study the effects of impurities in the imidazolium ILs on nanoparticle stability. In a later study, a new mode of stabilization was postulated where the presence of low amounts of 1-methylimidazole has substantial effects on the resulting stability of Au and Pd-Au nanoparticles in these ILs (Chemical Communications, 2009, 812). In further continuation of this study, a comparative study involving four stabilization protocols for nanoparticle stabilization in BMIMPF6 IL is described, and have shown that nanoparticle stability and catalytic activity of nanoparticles is dependent on the overall stability of the nanoparticles towards aggregation (manuscript submitted).<p> The second major project is focused on synthesizing structurally well-defined supported catalysts by incorporating the nanoparticle precursors (both alloy and core shell) into oxide frameworks (TiO2 and Al2O3), and examining their structure-property relationships and catalytic activity. a full article has been published on this project (Journal of Physical Chemistry C, 2009, 113, 12719) in which a route to rationally design supported catalysts from structured nanoparticle precursors with precise control over size, composition, and internal structure of the nanoparticles has been shown. In a continuation of this methodology for the synthesis of heterogeneous catalysts, efforts were carried out to apply the same methodology in imidazolium-based ILs as a one-pot media for the synthesis of supported-nanoparticle heterogeneous catalysts via the trapping of pre-synthesized nanoparticles into porous inorganic oxide materials. Nanoparticle catalysts in highly porous titania supports were synthesized using this methodology (manuscript to be submitted).

Due to the migration of scientists towards green chemistry, landfilling and incineration will no longer be acceptable options for plastics waste disposal in the future. Consequently new methods for recycling plastics and plastic products such as carpets are being researched. This study serves as a preliminary effort to study the catalytic feedstock recycling of polyolefins, specifically PP and PE, as source for gasoline range fuels, as well as an alternative for plastic waste disposal. Several studies have been conducted on the pyrolysis of waste polyolefins using commercial cracking catalysts (FCC), however, the effect of catalyst size and mode of catalyst dispersion have been studied sparsely. This thesis proposes to study these effects in the catalytic pyrolysis of polypropylene (PP), a component of carpets, using both fresh and used FCC catalysts. The same study will be applied to polyethylene (PE), which accounts for an enormous amount of municipal solid waste in the US today. Furthermore, the catalytic impact of calcium carbonate, a filler component of tufted carpet, will be investigated. Using thermogravimetric analysis, the global kinetics of the PP pyrolysis using various FCC catalysts will be derived and applied in the modeling of the pyrolysis reaction in a twin screw extruder. Furthermore, an economic analysis on the catalytic pyrolysis of PP is presented.

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Asymmetric hydrogenation as a general route to polypropionates has been explored for allylic alcohols, acids, and derivatives, which has led to the generation of 2,4-dimethylated hexane derivatives. Quantitative yields in most cases and enantioselectivities greater than 98% were obtained. A remarkable stereofacial inversion was observed when an ester or acid was present in the allylic position instead of an alcohol or alcohol derivative. This led to the construction of all four diastereomers of the hexanol series from a single enantiomer of hydrogenation catalyst. Also described are an attempted synthesis of (-)-lardolure, a formal synthesis of the methyl ester portion of the preen gland extract from the domestic goose Anser anser, and a total synthesis of an extract from the fungi A. cruciatus. The synthesis of these compounds demonstrated shortcomings of the known catalyst system showing enantioselectivities for polymethylated compounds was high, while diastereoselectivity was low. Methodology to develop new N-heterocyclic carbene catalysts was developed using the cyanide coupling of aldimines to generate electronically tunable 1,3,4,5-tetraaryl complexes, and X-ray, IR, and calculations were used to elucidate their electronic characteristics. These studies indicate that the 4,5-positions have as great an influence on the metal-ligand bond as the 1,3-positions. In addition, they are among the most electron-donating 2- metalated N-heterocyclic carbenes found thus far. An intrinsic relationship between catalytic activity and electron donating ability was found in transfer hydrogenations.

Transition metal catalyzed reactions have an important place in synthetic chemistry, but the mechanistic details for many of these reactions remain undetermined. Through a combination of experimentally determined 13C kinetic isotope effects (KIEs) and density functional theory (DFT) calculations, some of these reactions have been investigated. The cyclopropanation of an olefin catalyzed by rhodium (II) tetrabridged complexes has been shown to proceed through an asynchronous, but concerted mechanism. DFT does not provide an accurate transition structure for the reaction of an unstabilized carbenoid with an olefin, but it does predict an early, enthalpically barrierless transition state which is consistent with the reactivity of unstabilized carbenoids. For the case of stabilized carbenoids, the theoretical structures predict the KIEs accurately and a new model is proposed to explain the selectivity observed in Rh2(S-DOSP)4-catalyzed cyclopropanations. The chain-elongation step of atom transfer radical polymerization (ATRP) has been shown to be indistinguishable from that of free radical polymerization (FRP) for the CuBr/2,2??-bipyridine system. While DFT calculations predict an earlier transition state than observed, the calculations suggest that with increasing levels of theory the predicted KIEs come closer to the observed KIEs. A recently proposed [2 + 2] mechanism for the cyclopropenation of alkynes catalyzed by Rh2(OAc)(DPTI)3 has been shown not to be a viable pathway. Rather, the experimental KIEs are predicted well by canonical variational transition state theory employing the conventional mechanism for cyclopropenation via a tetrabridged rhodium carbenoid. DFT calculations also suggest an alternative explanation for the observed enantioselectivity. The 13C KIEs for metal-catalyzed aziridination have been measured for three separate catalytic systems. While the KIEs do not completely define the mechanism, all of the reactions exhibit similar KIEs, implying similar mechanisms. A surprising feature of this system is the presumed nitrene intermediate??s triplet spin state. This complicates the DFT analysis of this system.

This dissertation concerns the syntheses and characterization of supramolecules with quadruply bonded Mo2 4+ units, Mo2(DAniF)3 + (DAniF = N,N'-di-p-anisylformamidinate) or cis- Mo2(DAniF)2 2+, and chiral organometallic Rh2 4+ units, including racemic cis-Rh2(C6H4PPh2)2 2+ and pure enantiomers of cis-Rh2(C6H4PPh2)2 2+. Molecular pairs of dimolybdenum units in which Mo2(DAniF)3 + units are linked by cyclic diamidate anions or dioxolene anions have been investigated. Linkers impact the electronic communication between the dimetal units in various ways. The symmetry and the energy of the frontier orbitals of the linker are among the factors which influence significantly the properties of the molecular pairs. Nature has provided us a great opportunity to study quantitatively the equilibrium between neutral supramolecules with cis-Mo2(DAniF)2 2+ units. Studies of the concentrationdependent and temperature-dependent equilibria between a molecular triangle and square as well as a molecular loop and triangle using 1H and 19F NMR spectra provide quantitative values for the thermodynamic equilibrium constant K, as well as ∆Hº, and ∆Sº for the equilibria. The synthesis and characterization supramolecular compounds containing chiral cis- Rh2(C6H4PPh2)2 2+ units, including three racemic triangles and pure enantiomers of three triangles, a carceplex with T symmetry and two loops are also presented.

In the last few years the quest towards a hydrogen based economy has intensified interest for effective and less expensive catalysts for fuel cell applications. Due to its slow kinetics, alternative catalysts for the oxygen electroreduction reaction are actively researched. Platinum alloys with different transition metals (for example: Ni, Co and Fe) have shown improved activity over pure Pt. The design of a Pt-free catalysts is also highly desirable, and different alternatives including metalloporphyrins and Pd-based catalysts are being researched. Pd-based catalysts constitute an attractive alternative to Pt alloys in some fuel cell applications, not only because of lower costs but also because of the lower reactivity of Pt alloys towards methanol, which is important for improved methanol crossover tolerance on direct methanol fuel cells. In this work we apply density functional theory (DFT) to the study of four catalysts for oxygen electroreduction. The electronic structure of these surfaces is characterized together with their surface reconstruction properties and their interactions with oxygen electroreduction intermediates both in presence and absence of water. The energetics obtained for the intermediates is combined with entropy data from thermodynamic tables to generate free energy profiles for two representative reaction mechanisms where the cell potential is included as a variable. The study of the barriers in these profiles points to the elementary steps in the reaction mechanisms that are likely to be rate-determining. The highest barrier in the series pathway is located at the first proton and charge transfer on all four catalytic surfaces. This is in good agreement with observed rate laws for this reaction. The instability of hydrogen peroxide on all surfaces, especially compared with the relatively higher stability of other intermediates, strongly points at this intermediate as the most likely point where the oxygen bond is broken during oxygen reduction. This adds to the argument that this path might be active during oxygen electroreduction. A better understanding behind the reaction mechanism and reactivities on these representative surfaces will help to find systematic ways of improvement of currently used catalysts in the oxygen electroreduction reaction.

The recent finding that the FDA-approved antiobesity agent orlistat (tetrahydrolipstatin, Xenical) is a potent inhibitor of the thioesterase domain of fatty acid synthase (FAS) led us to develop a concise and practical asymmetric route to pseudosymmetric 3,4-dialkyl-cis-beta-lactones. The well-documented upregulation of FAS in cancer cells makes this enzyme complex an interesting therapeutic target for cancer. The described route to 3,4-dialkyl- beta -lactones is based on a two-step process involving Calter's catalytic, asymmetric ketene dimerization of acid chlorides followed by a facialselective hydrogenation leading to cis-substituted- beta -lactones. Importantly, the ketene dimer intermediates were found to be stable to flash chromatography, enabling opportunities for subsequent transformations of these optically active, reactive intermediates. Subsequent R-epimerization and R-alkylation or acylation led to trans- beta - lactones and beta -lactones bearing alpha-quaternary carbons, respectively. Several of the ketene dimers and beta-lactones displayed antagonistic activity (apparent Ki in the low micromolar range) in competition with a fluorogenic substrate toward a recombinant form of the thioesterase domain of fatty acid synthase. The best antagonist, a simple phenyl-substituted cis- beta -lactone, displayed an apparent Ki (2.5 ( 0.5 muM) of only 10- fold lower than that of orlistat (0.28 ( 0.06 muM). In addition, mechanistic studies of the ketene dimerization process by Reaction View infrared spectroscopy support previous findings that ketene formation is rate determining. A highly diastereoselective, nucleophile-promoted bis-cyclization process, employing readily available and tractable keto-acid substrates, is described. This methodology provides concise access to bicyclic- and tricyclic-beta-lactones bearing tertiary carbinol centers and quaternary carbons, greatly extending the scope of previous routes to bicyclic-beta-lactones from aldehyde acid substrates. This and related processes may be revealing a subtle interplay between [2 plus 2] cycloaddition and nucleophilecatalyzed aldol lactonization (NCAL) reaction manifolds. An early induction period in the bis-cyclization of keto-acids is confirmed via isolation of the complex between 4- pyrrolopyridine and Modified Mukaiyama reagent N-propyl-2-bromo pyridinium triflate. Dyotropic rearrangements of tricyclic keto beta-lactones derived in high yields and >19:1 diastereoselectivity from readily available 1, 3-dione acids is described. Zn (II) salts were found to be most efficient for affecting dyotropic 1, 2-acyl migrations where as sub stoichiometric TMSOTf was found to execute a delta-lactone migration providing bis gamma-lactone in modest yields. Enantioselective desymmetrization with inexpensive (S) - tetramisole has been demonstrated to provide direct evidence of Lewis base involvement in the Nucleophile Promoted Bis-cyclization of keto-acids. Further studies using TsCl as the carboxylate activating agent instead of modified Mukaiyama reagent and catalytic tetramisole are described for achieving practical, catalytic, enantioselective synthesis of beta-lactones from keto-acids. Preliminary studies toward conjugate addition- lactonization pathway provided a hint as to the complexity involved to affect this transformation under the bis-cyclization conditions. An alternate hypotheses concerning the possibility of isomerization-dienolate formation - lactonization is experimentally proven. Additionally, applications of these and related findings in the intramolecular Morita-Baylis-Hillman reaction with cyclic ketones have been investigated which provide new avenues of synthetic methodology development.