M.Sc. / This dissertation describes the synthesis and characterization of CdSe/ZnO and Ag/ZnO core/shell nanoparticles using water as a solvent. The effects of the concentration of the shell precursor, pH, and stabilizing agents on the properties of the nanoparticles were investigated. In general, the type of capping agents had an influence on the crystallite size of the core nanocrystals. The particle size distributions which were calculated from TEM images show that thioglycolic acid as a capping agent produced larger particle sizes compared to thioglycerol. For example, thioglycolic acid produced on average 5.0 nm CdSe nanoparticles while 4.0 nm average CdSe particle size was obtained when using thioglycerol as stabilizer. This observation was confirmed by UV/Vis absorption results which showed that thioglycerol capped CdSe NCs exhibited excitonic peaks positioned at lower wavelength than thioglycolic capped CdSe NCs. XRD results showed that the capping agents used in the current work had no influence upon crystal structure of the CdSe nanocrystals as the cubic structure was obtained with both stabilizers. The effect of shell precursor concentration at pH 12 showed heterogeneous formation of ZnO nanoparticles at high shell precursor concentrations. Various ZnO morphologies including nanoflowers and nanotriangles were observed on TEM images when 50 mL and 25 mL of zinc nitrate solution were used as shell precursors. UV/Vis absorption results also confirmed the presence of ZnO absorption peaks for samples prepared with 50 mL and 25 mL of zinc nitrate solution as shell precursors. PL results showed an increase in peak intensity as a function of precursor volumes. XRD results showed diffraction patterns due to the wurtzite structure of ZnO. CdSe diffraction patterns in these samples were not detected by the XRD instrument. At low volume of the shell precursor, which was 5 mL of 0.05 M zinc nitrate, TEM results showed that spherical CdSe/ZnO core/shell nanoparticles were obtained at pH 12 with 5 mL of 0.05 M zinc nitrate solution and 0.1 M sodium hydroxide used as shell precursor solutions, and thioglycerol as a stabilizer. XRD analysis of the v sample exhibited ZnO diffraction patterns and the CdSe patterns were not detected owing to their low peak intensities compared to those of the ZnO. Similar results were obtained when thioglycolic acid was used a stabilizing agent. However, TEM images showed the hexagonal shape of the CdSe/ZnO core/shell nanoparticles. The pH level was found to influence the photoluminescence properties of the CdSe/ZnO core/shell nanoparticles. The enhanced PL intensity was obtained with CdSe/ZnO core/shell nanoparticles with pH 9 in comparison with CdSe/ZnO core/shell nanoparticles prepared at pH 12. TEM images showed the presence of a thin ZnO shell on the surface of CdSe cores for CdSe/ZnO prepared at pH 9 which could be attributed to the PL enhancement. Although EDS results confirmed the presence of elements such as Cd, Se, Zn and O for both the CdSe core and ZnO shell, the XRD results confirmed the presence of only CdSe diffraction patterns, which suggested the ZnO shell had low peak intensity or was amorphous. A similar effect of these capping agents was observed for Ag nanoparticles as thioglycerol produced average particle size of 16.0 nm whereas 31.0 nm as the average particle size was obtained with thioglycolic acid as stabilizing agent. The crystal phase of Ag NPs was independent of the type of stabilizer. The Ag NPs precipitated in face centred cubic phase. Core/shell Ag/ZnO nanoparticles were produced with 5 ml of zinc nitrate as shell precursor. Higher volumes (50 ml and 25 ml) of zinc nitrate shell precursor induced heterogeneous precipitation of ZnO nanoparticles. XRD patterns confirmed peaks due to ZnO and Ag for Ag/ZnO core/shell nanoparticles.

Dit wil voorkom asof metallasiekels ‘n betreklike nuwe generasie van kataliste is, wat nie volkome vir gebruik in die industrie bestudeer is nie. Meeste van die bekende metallasiekels is fosfor, en tot ‘n mindere mate, swael gebasseerde mono- en bidentate metallasiekels. Relatief min is bekend oor die ooreenkomstige stikstof gebasseerde metallasiekels. Die doelwit van hierdie studie was om vas te stel of metallasiekels van stikstof en swael ligande vergelykbaar is met metallasiekels van fosfor ligande en of enige van dié vergelyk kan word met die standaard palladium en fosfor kataliste wat gewoonlik in situ berei word. ‘n Paar probleme wat ondervind is met organometaal literatuur was, onderandere, ‘n gebrek aan volledige eksperimentele prosedures vir metallasiekel sintese asook ‘n tekort aan volledige karakteriseringsdata. Metallasiekelvorming behels die insersie van ‘n metal in ‘n geaktiveerde C-H binding. Organometaal literatuur beskou metallasiekel vorming as oksidatiewe addisie gevolg deur redutiewe eliminasie. Meganisties gesproke het hierdie terme nie veel betekenis nie. Dit is egter moontlik om die reaksie te rasionaliseer in terme van suur/basis interaksies asook elektrofiliese substitusie wat nie die metal se oksidasie toestand verander nie. Die kritiese afhanklikheid van palladasiekel vorming op die reaksiekondisies het duidelik geword gedurende die studie. Die vorming van metallasiekels van palladium is altyd in kompetisie met ander prosesse soos kompleksasie en reduksie van palladium(II). Direkte metallering met palladium asetaat was net suksesvol met fosfor ligande, terwyl palladium chloried weer net suksesvol met stikstof ligande was. Die asetaatioon speel ‘n baie belangrike rol, naamlik om as basis op te tree. Palladium chloried het nie sulke sterk basiese eienskappe nie en dus misluk palladasiekel vorming met fosfor ligande. Wanneer hierdie feite in ag geneem word, is dit duidelik hoekom dit so moeilik was om die swak beskryfde literatuur metodes te volg. Sommige metallasiekels kan nie deur direkte insersie berei word nie en moet dus deur oksidatiewe addisie van halogeen verbindings gevorm word. Kermerkende verskille tussen die KMR spektra van die metallasiekel en sy vry ligand maak dit moontlik om te onderskei tussen die vorming van eenvoudige komplese en die metallasiekel. FAB-MS karakterisering is ook ‘n goeie metode om die verloop van metallering to moniteer. Die bereide metallasiekels en die standaard Pd(OAc)2/PPh3 sisteem is met mekaar vergelyk as katalisatore in die Heck reaksie. Met ‘n ariel jodied as, toon die stikstof palladasiekels hoër aktiviteit as die fosfor palladasiekels, terwyl hul aktiviteit vergelykbaar is met die standaard nie-palladasiekel kataliste. Die pinser komplese het amper geen aktiviteit onder hierdie kondisies getoon nie. Wat die meganisme van die reaksie betref, is bewyse vir die omsetting van die palladasiekel na ‘n palladium(0) spesie al aangevoer, maar meeste outeurs verkies ‘n meganisme wat ‘n Pd(II)/Pd(IV) oksidatiewe verandering behels. Twee tipes reaksies wat van groot belang is vir Sasol is isomerisasie en hidroformilering/alkoksikarbonilering van alkene. Daar is gevind dat palladasiekels oneffektief is in die reaksies met koolstof monoksied, omdat hulle gereduseer word na palladium(0). Die moontlikheid dat hierdie verbindings kan optree as kataliste in hidrogenasie reaksies is dus onwaarskynlik. Palladasiekels hou tog belofte in as kataliste vir olefien isomerisasie. Wanneer die katalitiese eienskappe van metallasiekels bestudeer word, is dit duidelik dat metallasiekels ‘n verandering in oksidasie toestand ondergaan as deel van die katalitiese siklus. In gevalle waar ‘n Pd(II) na Pd(IV) oksidasietoestand verandering moet plaasvind, sal dit noodwendig ‘n baie hoë energie proses wees. Dit sal dan die lae tempo van kataliese verklaar. Dus is dit amper seker dat metallasiekels beperkte toepassing sal vind in die industrie. Die vermoë van metallasiekels om as kataliste op te tree in reaksies waar ‘n verandering in oksidasie toestand nie nodig is nie, is to dusver nog nie ondersoek nie. / Prof. C.W. Holzapfel

In this study polar ligands that would be suitable for use in homogenous catalysis in aqueous-organic and/or ionic liquid systems were designed and synthesised. Initially an attempt was made to design a synthetic route that would incorporate an imidazolium into a phosphorus compound which would then allow the variation of the alkyl group on the imidazole or of the anion, thereby producing a series of ionic ligands with wide range of anticipated chemical and physical properties. This approach was partially successful: phosphines containing imidazolium moieties were synthesised by incorporating N-methyl imidazolium into bi- and tri-aryl phosphine compounds. As these ligands contain imidazolium residues, the retention of the catalyst in the ionic liquid to be used in the catalytic transformation would be enhanced. Water-soluble ligands that are suitable to aqueous-organic systems were also synthesised. The ligands were synthesised by first performing a Michael type reaction with diphenyl phosphine and a Michael acceptor, in this case, malonate esters. These were reduced and subsequently reacted with 1,4-butanesultone. The addition of butane sultone to these phosphorus compounds made them sufficiently water-soluble and therefore ideal for catalysis in aqueous biphasic or ionic solutions. Several water-soluble/ionic ligands were synthesised by incorporating dimethylphosphoryl chloride into di- and tri-aryl phosphine ligands in high yields followed by subsequent hydrolysis of the phosphonate groups. All the ligands produce were tested in transition metal-catalysed reactions, namely the Heck reaction, the Suzuki cross coupling and the Hydroformylation reaction. Test reactions were carried out under conditions selected to show the effectiveness of the ligands in the reaction, and they were performed in organic and aqueous-organic systems, as well as in ionic liquids for the Heck reaction. The results of these reactions were compared to the benchmark triphenylphosphine and it was found that the new ligands produced results that were similar to the triphenylphosphine but there were numerous instances where the new ligands produced better results. This study, therefore allowed for the synthesis for a range of polar phosphine ligands that would be suitable for homogenous catalysis using aqueous and/or ionic liquid systems, and these ligands were shown to influence transition metal-catalysed reactions. / Prof. D.B.G. Williams

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

Olefin metathesis is a powerful tool for assembly of carbon-carbon bonds. Amines and related N-donors are problematic functional groups in Ru-catalyzed olefin metathesis - a well- documented, but poorly understood problem. The first part of this thesis focuses on amine-induced deactivation pathways; two of which are described in depth. Alkylidene abstraction, a previously unknown reaction for nitrogen nucleophiles, was observed for smaller and less Bronsted-basic amines. Deprotonation of the metallacyclobutane intermediate formed during catalysis is prominent for highly Bronsted basic or sterically bulky N-donors. Monosubstituted (and, by extension unsubstituted) metallacyclobutanes are particularly vulnerable to deprotonation. For each pathway, the fate of the alkylidene Ru=CHR functional group proved key in determining the nature of deactivation. Both pathways have been detected during catalysis, as evidenced by formation of diagnostic amine (RCH2NR2’) or substituted propene products. A combination of quantitative NMR and GC-MS analysis was used to identify these species on loss of the Ru-alkylidene functional group. The second part of this thesis focuses on incorporating amines into catalyst design – an under-utilized strategy in the context of Ru-catalyzed olefin metathesis. A modified Grubbs-type catalyst was developed featuring a bulky, relatively non-basic biaryldiamine ligand. Metathesis activity for this catalyst was comparable, and in some cases superior to the most widely-used homogeneous catalysts currently available. Several new, related Ru-benzylidenes were also prepared and fully characterized in conjunction with the mechanistic studies described above. Progress toward development of N-anion-containing metathesis catalysts is also discussed. Synthesis of Ru-hydride complexes originally intended for this purpose allowed for a fundamental study of the coordination chemistry and reductive elimination chemistry of the NPh2– anion.

The large number of new heteronuclear bidentate ligands recently reported in the literature has unveiled a new area of research, namely that the use of different heteroatoms in bidentate ligands has led to new avenues towards more selective processes especially in asymmetric transformations. Instead of employing the traditionally used bidentate bisphosphine ligands, the dual objective of this study was therefore to design and synthesise P-N based bidentate ligands, and to apply these in catalytic transformations. A general route towards the synthesis of different series of P-N based ligands was followed. This path involved, as initial step, the condensation of o-diphenylphosphinobenzaldehyde with a series of primary amines to afford a series of iminophosphine ligands. Upon subsequent reduction of the iminophosphine ligands, a series of secondary aminophosphine analogues was obtained, and upon alkylation of the latter in the presence of a base, their tertiary aminophosphine derivatives were isolated. In these three series of ligands, the oxidation state of the nitrogen atom, as well as the degree of alkylation on this atom, was varied. These ligands were further elaborated by the incorporation of a second phosphorus atom to the already bidentate P-N ligands. This was achieved by reacting the secondary aminophosphine ligands with a base and chloro-diphenylphosphine. In order to vary the electronic nature of the newly introduced second phosphorus atom, a method for the incorporation of a dicyclohexyl phosphine moiety was developed. By introducing this group into the P-N backbone of these ligands, it was thus possible to electronically distinguish between two different phosphorus atoms in one ligand. Apart from the nature of the nitrogen and phosphorus atoms in these ligands, the use of different R-groups derived from the primary amines, enabled further variance in the inherent characteristics of these ligands: the variation in R-groups included aliphatic moieties, aromatic groups, and groups that contained additional heteroatoms. In these cases, the variation in R-groups thus also influenced the denticity of these ligands, which could render them more versatile in catalytic applications. In addition, a series of S-N based ligands, as well as some chiral P-N based ligands, was synthesised by using the previously-developed protocol. The oxygen sensitive nature of phosphines sometimes requires protection of these phosphines during different synthetic steps, and borane is often used for this purpose. However, deprotection of these phosphine ligands is required before they can be used in metal-catalysed reactions. As an adjunct to the present synthetic strategy, the concept of deprotecting phosphine-borane complexes such that new, extractable borane complexes are formed, was investigated, and formed a small part of this overall study. The deprotection of phosphine-boranes was performed using various “new” deprotecting reagents, and the borane species were separated from the free phosphines by using water / organic phase separations. The various extraction coefficients of the amine-borane complexes were determined. All the newly prepared heteronuclear ligands were used in a variety of catalytic transformations, including reactions catalysed by palladium, chromium and rhodium. The results obtained from these catalytic transformations indicated that most of these ligands afforded highly active catalysts in the different applications, and results were, in many cases, better than those obtained with commercially available ligands such as triphenylphosphine and dppp. To end off this study, an investigation towards the ó-donating properties of a selection of phosphine ligands was performed by converting the phosphines into their corresponding phosphine selenides, and calculating the 1J(77Se-31P) coupling constants. From this study, it was found that the electronic nature of different phosphine atoms in the same ligand could be characterised, and such information, in turn, can be used for the design of new ligands for specific catalytic systems. / Prof. D.B.G. Williams

The aim of this study was to investigate the mechanism of phosphine induced migratory carbonyl insertion in the monocyclopentadienyliron(II) carbonyl complex, [η5- (C5H5)Fe(CO)2Me], upon variation of different parameters such as the type and the concentration of the phosphine ligand and the solvent. The mechanism that agrees with the results obtained is presented below. / Prof. A. Roodt

The objective of the research described in this dissertation was the search for optimum ligand-metal complex combination that would facilitate the contrathermodynamic isomerisation of internal olefins. To this end a variety of ligands where synthesised and subsequently tested, firstly for their ability to isomerise alpha olefins and secondly their ability to isomerise internal olefins. Due to the lack of information obtainable from literature about catalytic isomerisation of olefins, the general reaction parameters had to be investigated. Various factors that could play a role in the isomerisation of olefins where investigated and these included the effect that solvents have on the isomerisation as well as the possibility of metalhydride formation. The possible formation of metal-hydrides was tested by adding a variety of acids and also the addition of hydrogen gas to the solution. All of these factors played an important role in the subsequent isomerisation of alkenes and valuable data could be obtained from these experiments. Solvents were found to have an effect on the isomerisation, but a trend could not be established. The effect of added acid was more pronounced and a correlation between acid strength and isomerisation could be established. It was also found that hydrogen gas added to the reaction mixture generally increased the reactivity of the metal catalysts and some experiments were done to optimise the use of hydrogen in these reactions. The use of commercially available ligands for the isomerisation reaction was also investigated and gave a broad indication of possible active ligands. After these initial reactions and information gathered from literature, it was decided to synthesise a set of di-imine ligands and also a set of bis-phisphite ligands. Due to tautomerism of the di-imines to the corresponding enamines, a set of enamine/imine ligands was synthesised and tested with two rhodium and two palladium catalysts. The synthesis of bis-phosphite ligands was initially problematic, but ideal conditions were found and a set of bis-phosphite ligands was synthesised and tested. Results obtained from the testing of both the enamine/imine lignds as well as the bisiii phosphite ligands were of value and a great many trends could be observed. Many of these observations had correlations to either the electronic nature of the various ligands as well as that of the metal centre. The testing of a set of palladium(II) metallocycles also gave an insight into the electronic properties necessary for the successful isomerisation of olefins. These electronic properties are always a combination of ligand and metal centre effects and thus a fine balance must be struck between these two factors. As a final conclusion to the work that was performed, internal olefins were subjected to tandem isomerisation-hydroformylation reactions using some of the more active metal-ligand systems. Internal olefins were isomerised and hydroformylated in the same reaction vessel to afford branched and linear aldehydes. In these reactions, it was proved that isomerisation as a primary reaction could be coupled to a secondary reaction and be of use in industry and further research in this field might prove to be of some value. / Prof. D.B.G. Williams

Several Schiff base ligands, N, N‟-(aryl)benzyaldiimine ligands (R-BEN); N, N‟-(aryl)benzyaldiamine dihydrochloride ligands (R-BENH•2HCl); N, N‟-(aryl)benzyaldiamine ligands (R-BENH); N, N‟-bis(cinnamaldiimine) ligands (R-CA2EN) were synthesized for the investigation of the electronic effect of the substituents at para-position of the Schiff base ligands and their copper complexes. The synthesis of Schiff bases was carried out by reacting a series of para-substituted benzyaldehyde, and para-substituted cinnamaldehyde with ethylenediamine. The imine group of Schiff bases, N, N‟-(aryl)benzyaldiimine ligands and N, N‟-bis(cinnamaldiimine)ligands were reduced to corresponding amines with sodium borohydride in methanol These ligands, N, N‟-(aryl)benzyaldiamine ligands (H-BENH), N, N‟-bis(cinnamaldiimine)ligands (CA2EN) were reacted with copper(II) dihalide and copper(I) monohalide ions respectively to form complexes. The ligands and their complexes were analysed using elemental analyses, FT-IR spectroscopy (mid-IR), UV/vis in aprotic and protic solvents,while mass spectrometry, 1H-NMR and 13C-NMR were used to further analyse the ligands. By using substituent parameters, both the single and dual substituent parameters with the spectroscopic data obtained from the spectroscopic techiques mentioned above, it was hoped to monitor and determine whether the electronic effects (resonance or inductive effcets) was predominantly within the Schiff base ligands and copper complexes. The NMR studies with dual substituent parameters suggest that the effects of the substituents are transimitted through the ligands, via resonance effects and that the phenyl group is nonplanar with the azomethine in N, N‟-(aryl)benzyaldiimine ligands. The presence of an extra double bond in Schiff base {(N, N‟-bis(cinnamaldiimine) ligand)} altered the electron density. The UV/vis studies showed that the symmetry of the N, N‟-bis(4-R-benzyl)-1, 2-diaminoethanedihalidecopper(II) complexes were predominantly tetrahedral for both chloro and bromo complexes. The correlation studies from mid-infrared were beneficial in monitoring the effect experienced by N, N‟-(aryl)benzaldiimine ligands, the studies suggest that the inductive effect is more pronounced at the C=N.

Magister Scientiae (Medical Bioscience) - MSc(MBS) / The synthesis and characterization of pyridinyl α-diimine Pd(II) complexes having a functionalized hydrocarbon attached to the imino nitrogen was performed. The catalytic activity of these complexes were then evaluated in the polymerization of ethylene and in the Heck coupling reaction of methyl acrylate with iodobenzene. Unconjugated β-diimine complexes of palladium were also synthesized and their activities towards ethylene polymerization and the Heck coupling of methyl acrylate and iodobenzene also evaluated and compared to that of the α-diimine complexes. Three of the α-diimine complexes synthesized showed activity towards ethylene polymerization, these being the complexes bearing the allyl, styrene and phenol functionalities. ω-Carboxylato complexes which were also synthesized showed no activity towards ethylene polymerization. The polymer produced was found to be high density linear polyethylene with an average PDI of 2.54 with Mn values ranging between 3.42 and 6.90 x 10-5 and Mw values ranging between 6.05 and 17.6 x 10-5. The complexes bearing the allyl, styrene and phenol functionalities, as well as the ω-carboxylato complexes active in the Heck coupling reactions of methyl acrylate with iodobenzene. None of the unconjugated β-diimine complexes prepared showed any activity towards ethylene polymerization even at high Al/Pd ratios. The activity of these complexes towards the Heck arylation reaction was comparable to that of the α-diimine complexes showing similar activities. / South Africa