With the growing demand for miniaturization of devices and for new materials with useful properties, the use of Chemical Vapor Deposition (CVD) for the manufacture of thin films is receiving growing attention. The synthesis of potentially volatile metal complexes and investigation of their use as CVD precursors is an important part of this process. The research presented addresses several major areas of this process, (i) the identification and synthesis of ligands which can impart volatility to a metal complex, (ii) the synthesis, characterization, and assessment of volatility of metal complexes containing these ligands, and (iii) the full materials characterization of thin films grown with these complexes. The use of trimethylphosphine, bis(trifluoromethyl)pyrazolate, and bis(trifluoromethyl)pyrrolyl ligands have been successfully used to synthesize volatile new complexes of cobalt, rhodium, and nickel, some of which show promise for use as potential CVD precursors. / text

published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Colloidal semiconductor nanoparticles (NPs) contain hundreds to thousands of atoms in a roughly spherical shape with diameters in the range of 1-10 nm. The extremely small particle size confines electron transitions and creates size tunable bandgaps, giving rise to the name quantum dots (QDs). The unique optoelectronic properties of QDs enable a broad range of applications in optical and biological sensors, solar cells, and light emitting diodes. The most common compound semiconductor combination is chalcogenide II-VI materials, such as ZnSe, CdSe, and CdTe. But III-V and group IV as well as more complicated ternary materials have been demonstrated. Coordinating organic ligands are used to cap the NP surface during the synthesis, as a mean of protecting, confining, and separating individual particles. This study investigated the impact of the ligand on particle growth and self-assembly into hierarchical structures. ZnSe QDs were synthesized using an aqueous route with four different thiol ligands, including 3-mercaptopropionic acid (MPA), thioglycolic acid (TGA), methyl thioglycolate (MTG), and thiolactic acid (TLA). The particle growth was monitored as a function of reaction time by converting the band gaps measured using UV-vis spectroscopy into particle sizes. A kinetic model based on a diffusion-reaction mechanism was developed to simulate the growth process. The growth data were fit to this model, yielding the binding strength in the order TLA < MTG ≈ TGA < MPA. This result showed the relationship between the QD growth rates and the chemical structures of the ligands. Ligands containing electron-withdrawing groups closer to the anchoring S atom and branching promoted growth, whereas longer, possibly bidendate, ligands retarded it. Removing TGA ligands from the surface of CdTe QDs in a controlled manner yielded new superstructures that were composed of either intact or fused particles. Purifying as-synthesized QDs by precipitating them using an anti-solvent removed most of the free ligand in solution. Aging this purified QD suspension for a week caused self-assembly of QDs into nanoribbons. The long time needed for self-assembly was due to the slow equilibrium between the ligands on QD surface and in solution. Accelerating the approach to equilibrium by diluting purifed CdTe QDs with organic solvents triggered rapid self-assembly of superstructures within a day, forming various nanostructures from nanoribbons to nanoflowers. The type of nanostructures that formed was determined by the solvation of TGA in the trigger solvent. Extracting the smallest portion of TGA in methanol promoted vectorial growth into ribbons consistent with dipole-dipole attractive and charge-charge repulsive interactions. Removing more of the TGA layer in IPA caused the dots to fuse into webs containing clustered ribbons and branches, and the directional nature of the superstructure was lost. Completely deprotecting the surface in acetone promoted photochemical etching and dissolved the QDs, yielding ower-like structures composed of CdS. Nanocrystal (NC) growth mediated by a ligand was also studied in the organic synthesis of FeS₂ nanocubes. Oleylamine was used not only as the ligand but also the solvent and reductant during the reaction. A one hour reaction between iron (II) chloride and elemental sulfur in oleylamine at 200 ℃ and a S to Fe ratio of 6 yielded phase pure pyrite cubes with dimensions of 87.9±14.1 nm. X-ray diffraction (XRD) spectra and Raman peaks for pyrite at 340, 375, and 426 cm⁻¹ confirmed phase purity. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) results showed that the oleylamine remained on the FeS₂ surface as a ligand. The reaction mechanism includes the production of pyrrhotite Fe₁₋ᵪS (0≤x<0.5) via reduction of S⁰ to S²⁻ by oleylamine and the oxidation of pyrrhotite to pyrite with remaining S⁰.

Controlling the absolute stereochemistry of molecules is a major challenge to contemporary chemists. Achieving high enantioselectivity with catalytic amounts of a chirality transfer (or inducing) agent, and the ease of regenerating such catalysts is yet another challenge. Due to the involvement of various transition metal complexes, the relatively young field of enantioselective catalysis has emerged as a powerful tool for organic chemistry. In our efforts towards the synthesis of a universal catalyst, O'Donnell Schiff base derived tetradentate ligands were shown to catalyze dialkylzinc additions to aldehydes in high selectivity. The three pot synthesis of bifurcated dipeptides in very good yields and the mechanistic aspects of diethylzinc additions to aromatic aldehydes are described in this dissertation. The chiral Lewis acidic behavior of these ligands was supported by a mechanistic study done examining the nonlinear effect. Unlike bidentate ligands such as (-)-3-exo-N,N-dimethylaminoisoborneol (DAIB), the tetradentate ligands in this study show strictly linear behavior. Also, the linear free energy relationships studied by observing the enantioselectivity with respect to electron donating or withdrawing substituents on the benzaldehyde substrates supported a Lewis acid role for the zinc complexes. A negative slope was obtained when ee's were plotted against sigma values of the substituted benzaldehydes. Since they bind to various bivalent transition metal cations, these ligands can be viewed as privileged structures, and may potentially become catalysts for various asymmetric reactions. As catalyst screening can be greatly facilitated by heterogeneous catalysis, solid phase ligands were synthesized using Wang and Merrifield resin supports. The synthetic methodology was developed using a diarylketimine linker with the aid of on-bead characterization techniques such as 13C NMR and UV-VIS spectroscopy. The ligands were shown to asymmetrically catalyze the alkenylzinc additions to aromatic aldehydes. In situ generation of alkenylzinc reagents by boron to zinc transmetalation followed by the addition to benzaldehyde in the presence chiral zinc complexes resulted in enantiomerically enriched allylic alcohols. The preliminary results for this transformation resulted in 3:1 selectivity in favor of S-isomer.

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La preparación de nuevos ligandos quirales P-OP (fosfina-fosfinitos y fosfina-fosfitos), fácilmente preparados con una estrategia sintética en dos etapas desde una aproximación covalente, es descrita en la presente Tesis Doctoral. El mejor catalizador de la serie ha demostrado tener propiedades catalíticas excelentes en la hidrogenación asimétrica catalizada por rodio de una amplia variedad de olefinas funcionalizadas. El resultado excelente y el diseño modular de los ligandos sintetizados hacen éstos muy atractivos para futuras aplicaciones.La presente Tesis Doctoral describe también la preparación de nuevos ligandos quirales que pueden comportarse como catalizadores supramoleculares inspirados en el mecanismo de regulación alostérica de los enzimas. / A library of enantiomerically pure P-OP ligands (phosphine-phoshinites and phosphine-phosphites) straightforwardly available in two synthetic steps from enantiopure Sharpless epoxy ethers is reported in the present PhD. Thesis. The "lead" catalyst of the series has proven to have outstanding catalytic properties in the rhodium-catalysed asymmetric hydrogenation of a wide variety of functionalised alkenes. Their excellent performance and modular design makes them attractive for future applications.This PhD. Thesis also reports the development of a practical route to chiral diphosphine ligands with supramolecular motifs, with potential for allosteric modulation, which we prepared for future catalytic studies.

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No description available.