Transition metal compounds such as Co₂(CO)₈ have often been used to catalyze various organic reactions. Severe difficulties may be encountered when attempts are made to recover and separate the soluble catalysts. A heterogeneous system consisting of Co₂(CO)₈ impregnated on zeolites with faujasitic structure has been designed and investigated using a variety of techniques. In situ FTIR spectroscopy and carbon monoxide evolution were used to identify the major products generated, namely Co₄(CO)₁₂ and Co(CO)_4^-. Disproportionation may be induced thus forming Co(CO)_4^- and an associated cation from the supported subcarbonyls by addition of various ligands such as methanol. The location of the supported cobalt carbonyls is determined by their reactivity toward various phosphines with various kinetic diameters. The materials prepared in this manner were found to be active in catalyzing the methanol carbonylation reaction and following thermolysis were also found to be active Fischer-Tropsch catalysts. Major products observed in the carbonylation of methanol were methyl acetate and an acetaldehyde dimethyl acetal. The supported cobalt catalyst displays greater activity than Co₂(CO)₈ in solution for the carbonylation reaction when conducted under similar conditions. In the Fischer-Tropsch process, selectivity is seen for the production of linear, short-chain hydrocarbons. / Ph. D.

This student is interested in reinvestigating the kinetics and mechanism of the bridged compound in l,2-dichloroethane with triisopropyl phosphite and in finding the reasons why the values of competition ratio k₋₂ /k₃ in this reaction are so large.

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Please see fulltext for abstract / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming

BDTBPMB has been proven to be an essential ligand in carbonylation chemistry. Its two tert-butyl groups and wide bite angle give it the ideal characteristics for this kind of chemistry, and leads to high activity and selectivity with use of its complexes. During this work the group of reactions where this ligand has been proven to be active has been extended with two new protocols for hydroxycarbonylation and aminocarbonylation. In the hydroxycarbonylation process, a large variety of unsaturated compounds were studied. Dioxane was found to be the ideal solvent, due to its properties in terms of coordinability, and miscibility with water. Using this solvent as the medium, a BDTBPMB complex of palladium was found to be highly active and selective under mild conditions. Initial attempts to address the aminocarbonylation of alkenes catalysed by the Pd/BDTBPMB system did not give high activity. This problem was overcome by the addition of an arylalcohol. Under those conditions, high selectivity and conversion was obtained in a wide variety of amides. However, attempts to address the aminocarbonylation of alkenes with ammonia gas to generate primary amides did not result in any conversion. The generation of these primary amides was obtained with transamidation of N-phenylnonamides which can be prepared by aminocarbonylation. Amides have been successfully hydrogenated to amines catalysed by a Ru/Triphos system. This system has been proven to be highly active in this reaction. High selectivities have been obtained in the generation of secondary amine. However, initial results of the hydrogenation of primary amides resulted in no formation of primary amines. A careful analysis of the mechanism of the formation of various products from the hydrogenation of primary amides allows the selective formation of primary amines by the ruthenium/Triphos system in the presence of ammonia. The possibility of the generation of primary amides in situ from acids under hydrogenation conditions, giving primary amines was explored with high conversion and moderate selectivities. To complete this work, a system based on a palladium complex for the decarboxylation of benzoic acids was developed. Usually, the decarboxylation reactions catalysed by copper require high temperatures. However, palladium complexes of highly electron donating ligands such as BDTBPMB or P([superscript]tBu)₃ were found to be highly active under milder conditions. This catalytic system was proven to be active in desulfonation reactions giving high conversion.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

M.Sc. (Chemistry) / Please refer to full text to view abstract

We report here the development of new and more general synthetic pathways for the preparation of allenyl and alkynyl carbonyls. These highly dense functionalized compounds were utilized as key intermediates for the synthesis of [3.2.1] and [3.3.1] bicyclic framework, the motifs found in many natural products. A convenient method described for the dehydration of ketoesters to generate conjugated and deconjugated alkynyl esters and conjugated allenyl esters. This sequential one-pot method involves the formation of a vinyl triflate monoanion intermediate that leads to the selective formation of alkynes or allenes depending on additives and conditions used. Product outcomes appear to be a function of unique monoand dianion mechanisms which are described. Our design of a Morita-Baylis-Hilman (MBH) reaction to include a fast silyl 1,3- Brook rearrangement has enabled the first ever anion-catalysis. This new reaction makes possible the addition of both aliphatic and aromatic aldehydes to s ilylallenes leading to carbinol allenoates. These new MBH reactions products allow for a fasttracked synthesis of [3.2.1] bisoxa-bicycles which make up the framework of many biologically active natural products including Vitisinol D. The development of cyclic addition of hydrazine nitrogen to unactivated alkynes catalyzed by non-metals is reported. Starting from readily accessible silyl allenyl esters, alkynyl hydrazines are prepared in one step and subsequently undergo unprecedented cyclization reactions in the presence of ammonium and phosphonium catalysts leading to dehydro-azaproline products. These heterocycles were also produced in high enantiomeric excesses using chiral ammonium phase transfer catalysts via a kinetic resolution pathway. / The racemic synthesis of fully functionalized bicyclic core of Vitisinol D was achieved using allenyl ester as a key intermediate. The required electron withdrawing group (EWG) at the position was screened for better addition followed by the compatibility towards successive transformation and, finally, the ease of removal. A reductive aldol method to transform lactone-enol to the desired [3.2.1] bicycle was extensively studied to understand the stereoelectronic requirements for the formation of such bicyclic structures. Due to the necessity of selective protection and deprotection of many phenolic and aliphatic hydroxyls as well as ester groups, orthogonal protecting groups were established accordingly. / by Pradip Maity. / Thesis (Ph.D.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

One microfiche--`Data from crystal structures solved by the author`--in pocket / Bibliography: leaves 172-174 / 174 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1987