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Please read the abstract in the section front of this document / Thesis (PhD (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted

Catalytic testing of polar amidophosphines: abstract A series of new nine arylruthenium complexes [(aryl)RuCl2(L)] was studied in isomerisations of allylic alcohols to carbonyl compounds. The best reaction conditions were found. The best solvent and reaction temperature were chosen. The best amount of catalyst and the best base and its amount were chosen too. In these conditions, the catalysts were tested for four substituted allylic alcohols. It was proven that these catalysts isomerise readily simple allylic alcohols, but not substrates that is highly substituted.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18950号 / 工博第3992号 / 新制||工||1615(附属図書館) / 31901 / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 松原 誠二郎, 教授 辻 康之, 教授 中尾 佳亮 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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<p>Uranium imido compounds have been traditionally studied due to their analogous nature to uranyl compounds. The investigation of uranium imido bonds can open the door to the activation of uranium oxygen bonds, which is important for the recyclization of spent nuclear fuel. This research encompasses further characterization of imido compounds utilizing electrochemical techniques which will better the understanding of these compounds. Utilizing what we already know about uranium imido compounds, further reactivity studies were conducted. Additionally, uranium is a suitable candidate for modeling synthesis of transuranic elements, specifically neptunium. Therefore, additional pathways to synthesize uranium tris(imido) and uranium tertrakis(imido) complexes were explored as a modeling system.  </p>

<p>Uranium imido complexes are highly sought after for their analogous nature to the uranyl moiety. Because of the highly reactive characteristics of uranium imido bonds compared to uranyl oxygen bonds these complexes have been used to investigate chemistry that can be used to activate the uranyl moiety. The activation of the <em>trans</em>-oxo groups of the uranyl moiety would open the door for the recycling of spent nuclear waste, diverting these chemicals from long term storage to a second life beyond nuclear fission. A suitable analog to the uranyl moiety has been discovered with the uranium bis(imido) family of complexes, these complexes can participate in chemistry that is similar if not, exactly the same as uranyl complexes. Studies with the uranium bis(imido) complex have been used to probe uranyl reactivity because the analogous nature of the two moieties. With that a uranium(IV) <em>cis</em>-bis(imido) complex was synthesized demonstrating how electron donation to the metal center can disrupt the Inverse Trans Influence (ITI) can as a result activate the <em>trans</em>-ligands on uranium. This complex is the first reported U(IV) bis(imido) with <em>trans</em> imido groups and achieved this geometry without large steric ligands to facilitate the <em>cis</em>- geometry. Computational analysis of this complex shows the stable nature of the geometry and how the fundamental electronics of this complex are the leading factor in the resultant geometry. When reactivity of the <em>cis</em>-bis(imido) was explored via protonation experiments a unique U(V) complex was isolated.</p> <p>Additional protonation reactivity was explored using UO2(tBubpy)(NTSA)2 with a variety of anilines to synthesize uranyl imido complexes. These experiments showed that the electronic environment—not the steric profile—of the anilines has a much greater effect on the stability of the resulting uranyl imido. The resulting uranyl imido complexes demonstrate the analogous nature of uranyl and uranium imido chemistry.</p> <p>Activation of the <em>trans</em>-imido groups on uranium bis(imido) complexes has also been shown with the synthesis of the uranium tris- and tetrakis(imido) complexes. These later complexes have shown that increased electron donation to the uranium metal center weakens and elongates the imido bonds, exposing these compounds to reactivity previously unavailable to uranium compounds with fewer multiply bound groups. </p>

<p>Cyclopropanes are found in an array of synthetic and natural products. The Simmons–Smith reaction has been one of the most common methods used to synthesize cyclopropanes since it was first discovered in the 1950s. The Simmons–Smith reaction entails the transfer of a carbene (:CH2) from a zinc carbenoid to an alkene, forming a cyclopropane. However, there are still many limitations to the Simmons–Smith method, including poor functional group tolerance and poor regioselectivity in polyalkene substrates. </p> <p>To address the weaknesses in the Simmons–Smith reactions, we have pursued a transition metal-catalyzed method. Our group has reported a cobalt pyridinediimine (PDI) catalyst system to carry out cyclopropanation reactions using gem-dichloroalkanes and gem-dibromoalkanes in order to access nonstabilized carbenes. This method also offers an advantage over diazo transfer chemistry since diazo chemistry requires a stabilizing group to be present in most cases.  This established work has demonstrated a complimentary reactivity to the Simmons–Smith reaction.</p> <p>In this work, we demonstrate that we could expand upon the existing methods of dimethylcyclopropanation to access spirocyclopropanated products by changing the identity of the dichloroalkane. In addition to this reactivity, an enantiopure catalyst that is able to catalyze an enantioselective cyclopropanation was found. We were able to show a broad scope of this new reaction, and mechanistic experiments are carried out in order to probe the mechanism of this reaction. Overall, this thesis offers a new way to access enantiopure dimethylcyclopropane and spirocyclopropanated products.</p>

The synthesis and characterization of novel complexes of silver supported by sterically demanding, highly electrophilic N-heterocyclic carbene (NHC) ancillary ligands, is described. Stable hydride, fluoride, alkoxide, alkyl, aryl, and alkynyl complexes are characterized by NMR spectroscopy and X-ray diffraction crystallography, and their reactivity is investigated. The interaction of silver centers in dinuclear complexes is probed by 109Ag NMR spectroscopy. Relevance to renewable fuel technology is demonstrated through the mediation of fundamental chemical transformations, including the heterolysis of hydrogen, the transfer of hydride to carbon dioxide, and the formation of carbon-carbon bonds. Kinetic studies shed light on the mechanism of hydrogen activation by hard-soft mismatched complexes of silver, and a formal catalytic cycle for the hydrogenation of carbon dioxide to formate derivatives is reported.