A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry. Johannesburg, 2015. / The selective hydrogenation of cinnamaldehyde (CALD), an α,β-unsaturated aldehyde, at the carbonyl (C=O) and olefinic (C=C) groups is an important reaction since its products mainly cinnamyl alcohol (CA) and hydrocinnamaldehyde (HCALD) are important intermediates for the production of many chemicals in a wide range of industries (pharmaceuticals, flavouring, agrochemicals, perfume). In this study the synthesis of nitrogen doped carbon spheres (NCSs) as catalyst supports for the hydrogenation of CALD is reported. At the heart of the hydrogenation of CALD is the catalyst, since it provides the surface for the various reactions to take place. In this study, an in-depth study was conducted on the NCSs support, by varying pyrolysis time, pyrolysis temperatures and flow rates of gases to determine the physical and chemical properties. The effects of chemically modifying the surfaces of the NCS supports by functionalization with acid and doping with carbon were also investigated. NCSs which had undergone different pre-treatments procedures were then deposited with Pd nanoparticles using different metal deposition methods and the resultant catalysts tested for the hydrogenation of CALD.

<p> The work describes the preparation and properties of some novel dibenzylideneacetone complexes of palladium and platinum. The structure and bonding in these complexes is discussed in view of their infrared and nuclear magnetic resonance spectra. The cyclotrimerization of acetylenes by zero-valent nickel complexes is discussed and the synthesis of a new cyclobutadiene-platinum complex is reported.</p> / Thesis / Master of Science (MSc)

No description available.

The carbopalladation process has been extended to form carbocyclic systems. The intramolecular version of the carbopalladation process stereospecifically generates fused bicyclic palladium complexes upon treatment of cis and trans methyl-S-methyl-2-carbomethoxy-7-thio-hept-5-en-l-oate with lithium tetrachloropalladate and potassium tertbutoxide in moderate yield. The cyclization of the corresponding amines, cis and trans methyl-N,N-dimethyl-2-carhomethoxy-7-amino-hept-5-en-1-oate, proceeded more rapidly and stereospecifically generate stable fused bicyclic palladium complexes in excellent yield. NMR studies revealed the bicyclic complexes generated in this manner resulted from a trans addition of palladium and the carbon nucleophile. Direct reduction with sodium borohydride (for sulfides) or hydrogen (for amines) resulted in cyclopentyl sulfides and amines in good to excellent yields. The reaction was extended to ketoesters and homoallylic amines to give a variety of cyclopentanoids. Extensions to larger ring systems yielded unstable palladium complexes. These complexes underwent oxidation at the amine functionality upon warming. Hydrolysis of the intermediate complexes yielded cyclohexyl and cycloheptyl aldehydes whereas reduction with hydrogen in the presence of molecular sieves gave cyclohexyl and cycloheptyl amines in excellent yields. Attempts at utilizing olefin mid carbon monoxide insertions to form macrocycles proceeded poorly, if at all. / Ph. D.

No / A new method for the synthesis of meso-substituted porphyrins is described: reaction of 5,10,15,20-tetrabromoporphine magnesium complex with aryl or heteroaryl boronic acids in the presence of Pd(PPh3)4 gave meso-substituted porphyrins in yields up to 70%.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 154-162).

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Low temperature fuel cells like proton exchange membrane fuel cells (PEMFC) are expected to play a crucial role in the future hydrogen economy, especially for transportation applications. These electrochemical devices offer significantly higher efficiency compared to conventional heat engines. However, use of exotic and expensive platinum as the electrocatalyst poses serious problems for commercial viability. In this regard, there is an urgent need to develop low-platinum or non-platinum electrocatalysts with electrocatalytic activity for the oxygen reduction reaction (ORR) superior or comparable to that of platinum. This dissertation first investigates non-platinum, palladium-based alloy electrocatalysts for ORR. Particularly, Pd-M (M = Mo and W) alloys are synthesized by a novel thermal decomposition of organo-metallic precursors. The carbon-supported Pd-M (M = Mo, W) electrocatalyts are then heat treated up to 900 oC in H2 atmosphere and investigated for their phase behavior. Cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements reveal that the alloying of Pd with Mo or W significantly enhances the catalytic activity for ORR as well as the stability (durability) of the electrocatalysts. Additionally, both the alloy systems exhibit high tolerance to methanol, which is particularly advantageous for direct methanol fuel cells (DMFC). The dissertation then focuses on one-pot synthesis of carbon-supported multi-metallic Pt-Pd-Co nanoalloys by a rapid microwave-assisted solvothermal (MW-ST) method. The multi-metallic alloy compositions synthesized by the MW-ST method show much higher catalytic activity for ORR compared to their counterparts synthesized by the conventional borohydride reduction method. Additionally, a series of Pt encapsulated Pd-Co nanoparticle electrocatalysts are synthesized by the MW-ST method and characterized to understand their phase behavior, surface composition, and electrocatalytic activity for ORR. Finally, the dissertation focuses on carbon-supported binary Pt@Cu and ternary PtxPd1-x@Cu “core-shell” nanoparticles synthesized by a novel galvanic displacement of Cu by Pt4+ and Pd2+ at ambient conditions. Structural characterizations suggest that the Pt@Cu nanoparticles have a Pt-Cu alloy layer sandwiched between a copper core and a Pt shell. The electrochemical data clearly point to an enhancement in the activity for ORR for the Pt@Cu “core-shell” nanoparticle electrocatalysts compared to the commercial Pt electrocatalyst, both on per unit mass of Pt and per unit active surface area basis. The increase in activity for ORR is ascribed to electronic modification of the outer Pt shell by the Pt-Cu alloy core. However, incorporation of Pd to obtain PtxPd1-x@Cu deteriorates the activity for ORR. / text

<p>This thesis presents the development of new palladium-catalyzed transformations involving synthesis and application of allylborane reagents. In these reactions various palladium sources, including pincer complexes and commonly used catalysts were applied.</p><p>A new transformation for allylation of aldehyde and imine substrates was devised using allyl acetates, diboronate reagents and catalytic amounts of Pd₂(dba)₃. By employment of commercially available chiral diboronates enantioenriched homoallyl alcohols could be obtained.</p><p>We have also developed a palladium-catalyzed method for synthesis of functionalized allylboronic acids from vinyl cyclopropane, vinyl aziridine, allyl acetate and allyl alcohol substrates using diboronic acid as reagent. In this process a highly selective selenium based pincer-complex was used as catalyst. The resulting allylboronic acid products were converted to potassium trifluoro(allyl)borates or allylboronates.</p><p>The functionalized allylboronic acids generated in the above procedure were employed as reagents in two synthetic transformations. One of these transformations involves a palladium(0)-catalyzed coupling reaction between allylboronic acids and aryl iodides. The reaction was regioselective for the branched allylic product, typically difficult to prepare in the absence of directing groups. We also developed another transformation for allylation of aldehydes with allyl alcohols via allylboronic acid intermediate. This procedure can be performed as a simple one-pot sequence affording homoallyl alcohols with excellent stereo- and regioselectivity.</p>

No description available.