The aim of the work was to develop an understanding of the phenomenon of rate enhancement observed when a heterogeneous catalytic reaction system is irradiated by ultrasound. The system under investigation was the catalytic hydrogenation of an a, B - unsaturated ketone, using zinc dust and aqueous nickel chloride as a source of hydrogen. When a slurry of zinc particles and aqueous nickel chloride is stirred or sonicated, nickel deposits in the form of patches on the surface of the zinc particles and simultaneously, zinc dissolves into the solution in the form of zinc ions, a process called pitting corrosion. Hydrogen atoms are formed when hydrogen ions diffuse from the bulk, adsorb onto the nickel surface and take up electrons generated by the dissolution of zinc. Once the atoms are formed on the surface, the atoms combine to form hydrogen molecules, which desorb in the form of hydrogen gas. When ketone is added to this slurry, the hydrogen atom formed on the surface of nickel is used as the source of hydrogen for the hydrogenation reaction. In these processes, nickel serves as catalyst. The ketone first has to diffuse to the bulk, adsorb onto the surface of nickel and undergo reduction by the hydrogen atoms to form the product. The product then has to desorb from the surface and diffuse into the bulk, in order to create vacant sites on the nickel surface for the adsorption of more ketone. Experiments dealing with measurements of hydrogen evolution rates pointed out that hydrogen is not a limiting reactant, since evolution was sustained for long periods of time. The evolution rates versus time data revealed that the nature of the plots for both, the stirred and sonicated systems were similar. These facts lead us to infer that the basic mechanism of nickel deposition, pitting corrosion, etc. was similar for the two cases. To study the hydrogenation reaction, experiments were first conducted keeping the nickel catalyst surface area constant. The results of these experiments showed that the hydrogenation reaction can be explained by a first order mechanism. Changing the speed of the stirrer did not effect the rate of the reaction; hence it was inferred that the reaction was not external mass transfer controlled. It was also seen that there was an no significant difference in reaction rates between the stirred and sonicated systems. Hence we conclude that sonication does not effect any process involved in the actual process of hydrogenation, i.e., adsorption, desorption, surface reaction, etc., do not get effected. It was concluded that the observed rate enhancements of similar compounds in the same system occur only when nickel catalyst is being continuously formed. This is possible only if irradiation with ultrasound enhances the rate of formation of the surface area of the nickel deposit. To study this phenomena, experiments were conducted with continuous formation of nickel catalyst. These experiments were conducted in three ways - stirring with zinc dust, sonication with zinc dust and stirring with presonicated zinc dust. For the first two kinds of experiments, the rates were low, increased to a maximum value and then decreased, but the nature of the third kind of experiments were different. The initial rates were very high as compared to either of the other two kinds of experiments but the rate rapidly reduces and becomes comparable to the rates obtained by stirring with zinc dust. We conclude that sonication creates many active sites on the surface of the zinc particles in the form of crystal defects, which are perhaps necessary for the deposition of nickel. When presonicated zinc particles are used, there are large numbers of these sites and these get consumed rapidly when stirred with aqueous nickel chloride solution. In this work, we do not deal with this case. In the case of sonication with zinc dust, these active sites are continuously created and are consumed by nickel deposition. For the stirred system, these sites are quite small to start with and new ones are not generated since there is no irradiation by ultrasound. Hence, the rates in the latter case are low for both nickel deposition and the hydrogenation reaction. In the model, it was assumed that the rate of increase of surface area of nickel, characterized by a specific rate term k z, was proportional to the amount of nickel in the bulk and also to the amount of free zinc surface area available. Similarly, nickel which deposits on previously deposited nickel (characterized by another specific rate constant, kn) was proportional to the amount of nickel in the bulk, the nickel area already deposited and also the free zinc surface area available. The model is in excellent agreement with the experimental data obtained. The model predicted higher values of kn and kz for the sonicated system, indicating that the rate of deposition of nickel is much higher in this case than for the stirred system. Moreover, the model also predicts that the deposit in the case of a sonicated system is thinner and flatter, since it was seen that the surface area created for the same amount of nickel deposited was much higher in this case than the stirred system.

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xiii, 122 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 100-103).

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Homogeneous organometallic species serve as useful catalysts for a vast number of chemical transformations. Ancillary ligands which bind to the metal center are employed to modulate the reactivity of the metal, and have been key to the discovery and improvement of most types of transition metal-mediated reactions. This thesis describes the design and application of P,N-ligands in platinum group-catalyzed reactions, specifically the Ru- and Ir-catalyzed ketone transfer hydrogenation (TH) and the Pd-catalyzed cross-coupling of aryl (pseudo)halides and N-H containing substrates. A zwitterionic Ru-species featuring a donor substituted P,N-indenide ligand was found to be an excellent catalyst for ketone TH, providing turnover frequencies (TOFs) as high as 300 000 h-1, while related cationic Ru-complexes ligated by P,N-indene ligands were found to be rather poor catalysts. Ir-complexes supported by either indene or indenide P,N-ligands were also found to be active TH catalysts (TOFs ~30 000 h-1), however phenylene P,N ligands, specifically (o-tBu2P-C6H4)NMe2, displayed optimal catalytic performance, allowing for rapid ketone reduction (TOFs of >100 000 h-1), at low catalyst loadings (as low as 0.004 mol% Ir). Enantioselective TH was achieved by employing the suitably substituted, commercially available P,N-ligand, Cy-Mandyphos in combination with [Ir(COD)Cl]2 and NaPF6. The use of P,N-ligands in Pd-catalyzed C-N cross coupling, specifically (o-R2P-C6H4)NMe2 (R = tBu or 1-Ad), allowed for the development of a highly versatile catalyst system for this reaction. In combination with [Pd(allyl)Cl]2 or [Pd(cinnamyl)Cl]2, the above described ligands enabled the cross-coupling of aryl and heteroaryl chlorides and bromides to a diverse range of amine and related substrates such as primary alkyl- and arylamines, cyclic and acyclic secondary amines, N-H imines, hydrazones, lithium amide, and ammonia. Reactions could be performed at low catalyst loadings (0.5-0.02 mol% Pd) with excellent functional group tolerance and chemoselectivity. The ligand N-[2-di(1-adamantylphosphino)phenyl]morpholine in combination with [Pd(cinnamyl)Cl]2 was found to provide excellent reactivity for the cross-coupling of ammonia to aryl chlorides with catalyst loadings of 0.3-5 mol% Pd. Sterically unbiased substrates containing electron-donating groups were tolerated with minimal competing diarylation. Aryl tosylates could be coupled with ammonia at room temperature and chemoselective ammonia arylation in the presence of other amine functionality was well tolerated. Pd-catalyzed cross-coupling of hydrazine with aryl chlorides and tosylates was achieved employing N-[2-di(1-adamantylphosphino)phenyl]-morpholine as the ligand. Good yields of the desired, mono-functionalized aryl hydrazine product was observed for a range of substrates at 5 mol% Pd. Selective hydrazine coupling was observed in the presence of other NH-functionality and NH-indazoles could be prepared by the tandem cross-coupling/condensation of hydrazine with 2-chlorobenzaldehydes.

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This thesis describes three types of reactions that were carried out using iridium catalysts. The first type is the iridium-catalyzed asymmetric hydrogenation of olefins. In paper I, the preparation of a new type of bicyclic thiazole-phosphine based iridium complex was described. The new catalysts have displayed high activity and enantioselectivity in the asymmetric hydrogenation of unfunctionalized olefins. Papers II and III focus on the expansion of the substrate scope for the iridium catalyzed asymmetric hydrogenation in which a number of heterocyclic olefins were evaluated. In paper IV, the enantioselective asymmetric hydrogenation of α, β-unsaturated esters was described. The chiral products bearing tertiary stereogenic centers obtained by hydrogenation have great synthetic value and have been used in the synthesis of pharmaceuticals as well as in the total synthesis of natural products. The second type is the asymmetric isomerization of allylic alcohols. In paper V, both cis and trans primary allylic alcohols were isomerized to the corresponding β-chiral aldehydes in high enantioselectivities by an N,P-chelating iridium complex. The third type is the selective mono-N-alkylation of amines with alcohols. In paper VI, a phosphine/NHC based iridium catalyst was synthesized and applied in the alkylation of amines. It is the first time that this type of transformation is carried out at room temperature.

Thesis (Ph. D.)--Michigan State University. Dept. of Chemistry, 2006. / Alpha in title represented by the lower case Greek letter. Title from PDF t.p. (viewed on Nov. 20, 2008) Includes bibliographical references (p. 235-245). Also issued in print.