No description available.

The stereochemical course of the Pd–catalyzed Suzuki-Miyaura cross-coupling of α-substituted, enantioenriched allylic boronic esters with phenyl iodide has been examined. The secondary boronic esters were prepared in both racemic and enantioenriched forms via borylationof a lithiated carbenoid with a geometrically defined vinyl boronic ester. The geometric purities were determined to be >99% and the enantiomeric excesses of stereodefined secondary boronic esters were found to exceed 98:2. In total, 8 allylic boronic esters were successfully cross-coupled, providing arylated products with high regioselectivities (>90:10) and complete enantiospecificities (>99%). The cross-coupling of a sterically and electronically unbiased, deuterated substrate confirmed that fully equilibrated π-allylic intermediates are not involved. Additionally, correlating the absolute configurations of the allylic boronic ester and the cross-coupling product allowed us to confirm that the transmetalation step of the reaction proceeded through a closed transition state via a syn-SE’ mechanism, which further suggests the importance of the distinct Pd-O-B bond linkage. Further, the cross-coupling of vinyl iodides to secondary boronic esters was investigated. / Thesis (Master, Chemistry) -- Queen's University, 2013-11-12 19:05:19.488

Little attention has been given to the formation of the putative PdL2 species required for Pd-catalyzed cross-coupling reactions. Active species are generally difficult to store due to air-sensitivity and are therefore formed in situ at unknown rates and in unknown yields via a variety of palladium precatalysts. Commonly employed Pd(0) and Pd(II) precatalysts are often relatively ineffective because they generate only low concentrations of the bis(phosphine) species PdL2 under most reaction conditions. This thesis describes the use of the easily synthesized and easily handled Pd(η3-1-Ph-C3H4)(η5-C5H5) (I) as a superior precursor than any other documented system for the in situ formation of PdL2. Rapid and quantitative formation of active catalyst solutions allow us to demonstrate that I is also the best precatalyst known for PdL2-catalyzed crosscoupling reactions. We discuss the Suzuki-Miyaura reaction of 4-bromoanisole with phenylboronic acid and demonstrate that, under mild reaction conditions, higher initial rates and higher conversions with I can be obtained compared with other common precatalysts (Pd(OAc)2, Pd(PPh3)4, Pd2dba3, etc.) containing a variety of phosphine ligands. This methodology has also been extended to other cross-coupling reactions, as we demonstrate that higher initial rates and higher conversions with I can be obtained for a variety of Mizoroki-Heck arylations and Buchwald-Hartwig aminations. / Thesis (Ph.D, Chemistry) -- Queen's University, 2013-06-25 11:53:06.75

The Fischer-Tropsch process in South Africa, used for producing chemicals from synthesis gas, which is mostly derived from the gasification of coal, gives a large amount of medium chain length alkanes (C4-C8), which have little commercial value. Internationally, industry has recently placed more focus on the conversion of alkanes to value-added products. Two important routes to achieving this are dehydrogenation and oxidative dehydrogenation. The latter is an economically feasible route, in which there is growing interest by the international research community, and was investigated in this study. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2007.

There is enormous interest in the design and development of efficient chiral ligands for asymmetric catalysis, as a result, this field has become one of the most popular areas of research in organic chemistry. This project involved the investigation of the novel chiral pentacyclo-undecane (PCU) diol 54a, PCU bisimine 87 and PCU bis(oxazoline) 100 type ligands. The PCU diol ligand was synthesized, but proved to be difficult to obtain enantiomerically pure which hindered further investigation into this type of ligand. The PCU bisimine ligand 87 was synthesized. However due to its instability it was not further pursued. Synthesis of the PCU bis(oxazoline) ligand 100 was successful. This ligand was complexed to various metal salts and its efficiency as a chiral Lewis acid catalyst was evaluated on the asymmetric Diels-Alder reaction between 3-acryloyloxazolidin- 2-one 52 and cyclopentadiene 33. The anhydrous magnesium perchlorate ligand complex emerged as the best catalyst providing the endo-cycloadduct product 53 in 81 % enantiomeric excess at -40 oC. Optimizations of the possible conformations of the magnesium complex of ligand 100 with the substrate 52 were performed using Density Functional Theory (DFT) calculations. The more energetically favoured complex conformation was established. The Re-face of the dienophile which was less hindered produced the product consistent with the experimentally observed product 16. Based on the calculated bond lengths from the computational model binding of the ether oxygen on the PCU moiety to magnesium was observed. All the novel compounds were fully characterized using NMR, IR and mass spectroscopy as the main tools. / Thesis (M.Sc.) - University of KwaZulu-Natal, Westville, 2008.

This thesis described the development of new catalytic system for the conversion of natural gas (methane) to liquid products such as methanol and formaldehyde. This technology can allow the exploitation of small and medium size gas fields without the need to build an expensive gas to liquid plants or long pipelines. The technology is based on a concept of non-separating membrane reactor where an inorganic membrane paper serves as a catalyst support through which a reaction mixture is flowing under mild conditions and short residence times.

No description available.

Recently established as an excellent activator for π-systems, efforts made in gold chemistry have increased enormously, resulting in a new ‘Gold Rush’ in chemistry. This thesis is a small contribution to it. There are two main aspects dominating the following chapters: gold catalysts bearing N-heterocyclic carbenes (NHCs) as supporting ligand, and H₂O assisted catalysis. The initial motivation for the presented work was to specifically demonstrate the potential of [(NHC)AuCl] as suitable catalysts for both known and new organic transformations and to establish these commercially available catalysts in gold chemistry, a field currently dominated by phosphine bearing gold complexes. Water mediated catalysis became the next repeatingly occurring aspect of this thesis by pursuing this initial aim and finding water as a useful solvent or agent, respectively. Various useful applications for gold-NHC complexes are presented, starting with the Meyer-Schuster rearrangement of propargylic alcohols as a continuation of the work realized with propargylic acetates by the Nolan group in early investigations on gold catalysts. Next, a study on alkyne hydration is presented with focus on low catalysts loadings to establish gold catalysts as a powerful choice for such a highly relevant reaction. The catalytic system is then advantageously adapted to a silver-free variation, still active at low catalyst loadings and with further mechanistic insight. Inspired by gold activation of alkynes, a gap of reactivity in gold catalysis is closed by a successful demonstration of nitrile hydration, a functionality previously thought to be inert towards gold activation. In this context, formation and role of dinuclear hydroxy-bridged gold complexes is investigated highlighting these complexes as a possible resting state of gold complexes in the presence of water. Next, the formation of furanones via alkoxylation/lactonization of propargylic propiolates is presented, an observation initially made when exploring the scope of the Meyer-Schuster rearrangement. The dissertation finally closes with the gold-catalyzed formation of amides, this time however achieved from aldoximes reacting via dehydration/hydration mechanism.

A set of mild conditions for the pentafluorophenylation of carbonyl compounds employing copper-bisphosphine catalysis have been developed. The optimised conditions allow access to a wide range of pentafluorophenyl benzyl alcohols in high yields. The reaction of aliphatic aldehydes and particularly electrophilic ketones to give products in moderate yields is also disclosed. An investigation into the reactivity of β-fluoroalkyl-α ,β -unsaturated carbonyl compounds was conducted. Asymmetric copper hydride reduction of β -fluoroalkyl-α , β-unsaturated ketones was found to preferentially give the allylic alcohol product resulting from 1,2 attack in up to 62% ee. Reaction of β-fluoroalkyl-α , β-unsaturated esters under similar conditions gave the product of conjugate reduction in higher enantiomeric excess; up to 99% was observed. Rhodium-catalysed arylation of β -fluoroalkyl-α , β-unsaturated ketones was also found to give the product of direct carbonyl attack. Conditions for the racemic reaction are described along with those for the enantioselective reaction of methyl ketones in up to 74% ee. Ruthenium catalysed arylation of β-fluoroalkyl-α ,β -unsaturated aldehydes employing Me-Bipam as ligand gave the desired secondary allylic alcohols in good yields and good to excellent enantiomeric excesses (14 examples, 76-87% ee).

The major part of this thesis concerns the development of catalytic methodologies based on palladium nanoparticles immobilized on aminopropyl-functionalized siliceous mesocellular foam (Pd0-AmP-MCF). The catalytic activity of the precursor to the nanocatalyst, PdII-AmP-MCF is also covered by this work. In the first part the application of Pd0-AmP-MCF in Suzuki-Miyaura cross-coupling reactions and transfer hydrogenation of alkenes under microwave irradiation is described. Excellent reactivity was observed and a broad range of substrates were tolerated for both transformations. The Pd0-AmP-MCF exhibited high recyclability as well as low metal leaching in both cases. The aim of the second part was to evaluate the catalytic efficiency of the closely related PdII-AmP-MCF for cycloisomerization of various acetylenic acids. The catalyst was able to promote formation of lactones under mild conditions using catalyst loadings of 0.3 - 0.5 mol% at temperatures of up to 50 oC in the presence of Et3N. By adding 1,4-benzoquinone to the reaction, the catalyst could be recycled four times without any observable decrease in the activity. The selective arylation of indoles at the C-2 position using Pd-AmP-MCF and symmetric diaryliodonium salts is presented in the third part. These studies revealed that Pd0-AmP-MCF was more effective than PdII-AmP-MCF for this transformation. Variously substituted indoles as well as diaryliodonium salts were tolerated, giving arylated indoles in high yields within 15 h at 20 - 50 oC in H2O. Only very small amounts of Pd leaching were observed and in this case the catalyst exhibited moderate recyclability. The final part of the thesis describes the selective hydrogenation of the C=C in different α,β-unsaturated systems. The double bond was efficiently hydrogenated in high yields both under batch and continuous-flow conditions. High recyclability and low metal leaching were observed in both cases. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Submitted.</p><p> </p>