Made available in DSpace on 2014-10-09T12:38:26Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:29Z (GMT). No. of bitstreams: 1 05827.pdf: 4162110 bytes, checksum: 4818bf19a034f75fcbef60b0310a8176 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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

D.Phil. / Palladium chemistry has advanced dramatically in the last few years, with a huge number of wide-ranging studies, particularly with respect to the application of palladium complexes as catalysts, having been performed. The discovery of the phenomenon of hemilability (the ability of a ligand to be bidentately coordinated but with one donor atom more weakly bound and thus able to decoordinate in the presence of a catalytic substrate) has further assisted the growth, since it has allowed a greater understanding of the mechanisms of catalytic-reactions. However, the focus of much of this work has been on ligands containing phosphorus and oxygen as potential donor atoms, with little attention being turned to ligands with other donor atoms. The current study concentrates on a series of palladium complexes containing potentially hemilabile thioether, selenoether and telluroether carboxylate ligands with the oxygen as the strongly coordinating atom. Each complex was completed by the palladium coordinating to a phenyl ligand trans to the oxygen of the hemilabile ligand and either one or two triphenylphosphine ligands, depending on whether or not the -hemilabile ligand was monodentately or bidentately coordinated. These complexes are of interest as possible catalysts for the oligomerisation of ethene, and had been previously synthesised and characterised by NMR spectroscopy, mass spectrometry and catalytic studies. In the current work the crystal and molecular structures of the various complexes were determined. Since a number of pairs of complexes containing the monodentate and bidentate forms of the ligands were identified the hemilability of the ligands was confirmed.

An electrochemical technique has been developed for the production of precursors to ceramic films on hydrogen sorbing metal substrates. It involves the electrolysis of aqueous metal salt solutions which yields hydrogen at the cathode, resulting in local generation of base (hydroxide ions) around this electrode. Such conditions promote the precipitation of metallic hydroxides from a suitable electrolyte. If the local alkaline environment is not disrupted by convective or other forces, then a solid phase accumulates near the cathode, and forms an adherent gel-like structure on its surface. In order to maintain deposition, it is essential that gaseous hydrogen evolution is minimised, and preferably eliminated. This can be achieved by use of a hydrogen sorbing cathode material, such as palladium. The electrode, and adherent film (or, in appropriate circumstances, the deposit alone) can then undergo a subsequent calcination treatment to yield the ceramic layer. It is possible to generate both porous and compact structures by this method, depending on the potential programme employed during deposition. Research has been conducted into the understanding of mechanisms involved in porosity control of films deposited during different potential regimes, with view to establishing routes to layers of predetermined physical structure. In-situ optical methods were employed to complement the electrochemical techniques, providing valuable insight into the initial mechanisms of film formation and the subsequent thickening processes. The utility of the precipitation process was illustrated by the fabrication of films which demonstrated a variable conductivity over a range of humidities appropriate to sensing application. Investigation into the use of a bipolar palladium electrode as an aid to generating thick film deposits was carried out. The device comprised a palladium plate, operated as a bipolar electrode in aqueous electrolyte. Under suitable conditions, the negative face of this electrode can be made to generate and absorb hydrogen, whilst simultaneously, the positive face oxidises hydrogen transported across the bipolar substrate by diffusion. Thus the cathode face is a non-gassing electrode on which thick deposits of metal hydroxide can be grown. This line of research lead to the realisation of a self-feeding hydrogen anode at the electrode's positive face. Further research was undertaken to assess the electrochemical properties of this anode. The effective operating window for hydrogen oxidation was investigated, and the effect of prolonged potential cycling, elevated temperature and bipolar plate thickness on this region was also considered.

>Magister Scientiae - MSc / Supercapacitors are one of the important subjects concerning energy storage which has proven to be a challenge in this country. Currently, the electrodes of most commercial supercapacitor are made of carbon which is known to be inexpensive and has high resistance to corrosion. These carbon based supercapacitors operate under EDLC. They offer fast charging/discharging rates and have the ability to sustain millions of cycles without degrading. With their high power densities, they bridge the gap between batteries which offer high energy densities but are slow in charging/discharging and conventional dielectric capacitors which are very fast but having very low energy densities. The objective of this work was to develop a high performance supercapacitor using polyanilino-graphene oxide intercalated with platinum group metal nanocomposites. Specific capacitance of each material was investigated with the objective of ascertaining the material that has the best capacitance. In this work, GO was functionalized with aniline and intercalated with Pt, Pd and Pd-Pt nanocomposites. The nanomaterials were characterized with FTIR, Ultravioletvisible (UV-visible) spectroscopy, high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscopy (HRTEM), energy dispersive x-ray microanalysis (EDS) and X-ray diffraction (XRD) analysis. The composites were tested for possible application as supercapacitor materials using potentiostatic-galvanostatic constant current charge/discharge. The synthesized materials had good electronic, mechanical, optical, physical etc. properties as proven by the various characterization techniques but they proved not to be ideal for application as supercapacitor materials. The materials tested negative when tested for both anodic and cathodic materials therefore we can conclude that the materials are not good supercapacitor materials and therefore cannot be used in application as novel as supercapacitors.

D.Sc. (Chemistry) / The aim of this study was directed towards the stereo- and regiospecific introduction of carbon nucleophiles onto the 1- and 4-positions of glycopyranosides, since these chiral molecules contain the tetrahidropyran skeleton of a wide range of biologically active compounds (example the carpenter bee pheromone or the civit cat pheromone) or substructures of more complex natural products, such as the ionophore antibiotics indanomycin and zincophorin. Two appraoches for the introduction of carbon substituents onto the 1- and/or 4-positions of unsaturated glycopyranosides were investigated ...

M.Sc. / The dimeric structure of Lawesson’s reagent, (RPS2)2 (R = 4–MeOC6H4), or its ferrocenyl analogue (R = ferrocenyl, Fc) leads to symmetrical cleavage through nucleophillic attack by alcohols to form dithiophosphonic acids, which can be readily deprotonated by ammonia to form the corresponding ammonium salts, which can be further reacted with transition-metal halides to form new metal complexes. Among the phosphor-1,1-dithiolates as a generic class of compounds, the dithiophosphates, [S2P(OR)2]-, have been most intensely studied and the dithiophosphonates [S2PR(OR’)]-, the subject of the present study, to a far lesser extent. In this study, a large variety of new dithiophosphonate salts were synthesized from diverse alcohol functionalities derived from cholesterol, estrone, estradiol, pentaerythritol, ethandiol, hydroquinone, resorcinol, glucose and ribose. The salts were oxidized with iodine to yield various S-S oxidative products, of which two X-ray crystal structures of such compounds, the ethandiol and pentaerythritol derivatives, were obtained and they were subjected to further investigation by cyclic voltammetry due to the ferrocenyl-rich functionalities they contain. The reaction of these [S2PR(OR’)]- type salts with a number of gold(I) and palladium(II) precursors, yielded a variety of new complexes. The compounds containing multiple alcohol (hydroxy) sites have been reacted with gold(I) and palladium(II) starting materials ClAu(tht) and PdCl2(PPh3)2, respectively and also with other gold(I) variants, including the mono- and dinuclear phosphines ClAuPPh3, Au2Cl2dppe and Au2Cl2dppa. A new X-ray single crystal structure of a gold(I) complex could be obtained as a decomposition product. New products have been characterized through a combination of solution 1H and 31P NMR, EIS mass spectrometry, IR, elemental analysis, electro-chemistry and single crystal X-ray crystallographic studies.

This thesis presents the synthesis, characterization and reactivity of a series of palladium complexes that contain redox-active verdazyl ligands. This work was motivated by the possibility of discovering new and interesting reactivity that may eventually lead to the development of new chemical reactions. A bidentate verdazyl radical ligand that contains an aryl phosphine was synthesized. Reaction of this ligand with (PhCN)2PdCl2 yielded a square planar (verdazyl)PdCl2 complex. Structural and spectroscopic data suggest that this compound consists of a ligand-centered radical coordinated to a Pd(II) center. The radical complex was chemically reduced by one-electron to generate a binuclear chloride-bridged [(verdazyl)PdCl]2 complex. In this reduced complex, both metals were still Pd(II) and the verdazyl ligand was determined to be in its singly reduced, monoanionic charge state. The original radical PdCl2 complex could be regenerated via one-electron oxidation of the reduced complex using PhICl2. The verdazyl ligands in the reduced complex could also be reversibly protonated to generate “leuco” verdazyl complex (verdazyl-H)PdCl2. Reaction of the radical (verdazyl)PdCl2 complex with water triggers a ligand-centered redox disproportionation reaction. A series of bis(verdazyl) palladium complexes were synthesized using a bidentate pyridine-substituted verdazyl ligand. Reaction of two equivalents of radical ligand with (CH3CN)4Pd2+ yielded a (verdazyl)2Pd(solvent)2+ complex (solvent = CH3CN or DMSO). In this complex, one verdazyl radical ligand chelates to palladium and the other binds as a monodentate ligand. Two-electron reduction of this complex generated a (verdazyl)2Pd complex in which two monoanionic verdazyl ligands are bound to a central Pd(II) ion. This reduced complex could also be made via reaction of 0.5 equivalents of Pd(0)2(dba)3 with two equivalents of radical ligand. In this reaction, the metal is oxidized by two electrons and each ligand is reduced by a single electron. Two-electron oxidation of the reduced complex in the presence of DMSO yielded the original bis(radical)complex, (verdazyl)2Pd(DMSO)2+. Chlorination of the reduced complex using one equivalent of PhICl2 (two-electron oxidation) resulted in dissociation of one verdazyl ligand to afford a 1:1 mixture of free verdazyl : (verdazyl)PdCl2, in which both of the verdazyls are neutral radicals. Reaction of the reduced complex with 0.5 equivalents of PhICl2 (one-electron oxidation) yielded a (verdazyl)2PdCl complex that contained a bidentate reduced verdazyl ligand and a monodentate radical ligand. All three of the oxidation reactions described above adhere to ligand-centered redox chemistry. Reaction of the reduced (verdazyl)2Pd complex with excess HCl resulted in protonation of both the anionic verdazyl ring and the pyridyl group to generate a leuco/pyridinium tetrachloropalladate salt, (verdazyl-H2)2(PdCl4). The protonated salt could be converted back to the original (verdazyl)2Pd complex by deprotonation with water. Palladium complexes of a tridentate NNN-chelating verdazyl ligand were prepared and their redox chemistry was explored. Reaction of the radical ligand with (CH3CN)4Pd2+ yielded radical complex (verdazyl)Pd(NCCH3)2+. The tridentate ligand was also prepared in its reduced, leuco form (verdazyl-H). Reaction of the leuco verdazyl with (CH3CN)2PdCl2 generated HCl and a (verdazyl)PdCl complex in which the ligand is in its monoanionic charge state. The reduced (verdazyl)PdCl complex was reacted with AgBF4 to afford (verdazyl)Pd(NCCH3)+ via chloride abstraction; the verdazyl remained in its reduced charge state following the reaction. Both reduced complexes (chloro and acetonitrile) were oxidized by a single electron to afford the corresponding radical complexes. These radical complexes could be reduced by a single electron to regenerate the original reduced complexes. Like the previous two projects, all of the redox chemistry was ligand-centered. The reactivity of these complexes with primary amines was also explored. Reaction of radical complex (verdazyl)Pd(NCCH3)2+ with n-butylamine resulted in one-electron reduction of the verdazyl ligand. We were unable to determine the mechanism of the reaction, but the reactivity that was observed demonstrates the potential for verdazyl-palladium complexes to be used in the design of new radical reactions. / Graduate / 2018-07-17

A new series of aminomethylphosphine ligands incorporating a PCN backbone and a pendant amine were synthesised using a phosphorus Mannich condensation reaction. Their coordination capabilities were investigated with late transition metal centres. Following a procedure well established within our research group, several phosphines were obtained using {P(CH2OH)4}Cl (THPC) in two steps. Firstly, THPC was reacted with various ortho and para anilines to give phosphonium salts P{CH2N(H)R}4Cl (R = C6H5, o-MeC6H4, o-i PrC6H4, o-t BuC6H4, o-FC6H4, o-CF3C6H4, o-{C(Me)=CH2}C6H4, p-MeC6H4, p-i PrC6H4, p-FC6H4 and p-EtC6H4). Secondly, these new salts were reacted with Et3N to obtain the cyclic RN(H)CH2P{(CH2)3(NR)2} phosphines (R = para-substituted anilines) or with KOt Bu to obtain acyclic P{CH2N(H)R}3 phosphines (R = ortho-substituted anilines) and cyclic P{CH2N(R)CH2}2P diphosphines (R = ortho-substituted anilines). Double condensation was observed in the 31P{1 H} NMR of cyclic phosphines RN(H)CH2P{(CH2)3(NR)2} to form {(CH2)3(NR)2}PCH2N(R)CH2P{(CH2)3(NR)2} diphosphines. Some cyclic phosphines were investigated under a wide range of conditions with Ph2PCH2OH giving asymmetric Ph2PCH2N(R)CH2P{(CH2)3(NR)2} diphosphines along with symmetric diphosphines counterparts and other phosphorus coproducts according to 31P{1 H} NMR and MS. A novel bicyclic OP{CH2N(R)CH2}3PO diphosphine (R = p-MeC6H4) was obtained as crystalline solid from the filtrate of the reaction between RN(H)CH2P{(CH2)3(NR)2} and Ph2PCH2OH and it was characterised by X-ray spectroscopy. Attempts to synthesise this diphosphine from P(CH2OH)3 and p-MeC6H4 were unsuccessful. The family of aminomethylphosphine ligands was extended by treating Ph2PCH2OH or CgPCH2OH (Cg = 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phosphaadamantane) with various primary amines to afford R(H)NCH2PR'2 (R' = Cg or Ph). Symmetric Ph2PCH2N(R)CH2Ph2 diphosphines were observed in the 31P{1 H} NMR spectra indicating that phosphines with Ph2P-moiety were more susceptible to undertake a second condensation. Novel asymmetric o-{Ph2PCH2C(H)(CH3)}C6H4N(H)CH2PPh2 diphosphine was synthesised by treatment of o-{C(Me)=CH2}C6H4NH2 with Ph2PH to afford o-{Ph2PCH2C(H)(CH3)}C6H4NH2 followed by condensation of the amino group with Ph2PCH2OH. Analogous o-{CgPCH2C(H)(CH3)}C6H4NH2 phosphine was also obtained. The coordination capabilities of selected compounds was studied with late transition metal precursor such as Pt(II), Pd(II) and Ru(II). Monophosphine compounds acted as Pmonodentate ligands to form square planar cis and trans MCl2L2 (M = Pt and Pd) complexes. However, whereas cyclic ligands RN(H)CH2P{(CH2)3(NR)2} afforded cisMCl2L2, acyclic ligands P{CH2N(H)R}3 afforded trans-MCl2L2 along with cis-PtCl2L2 in some cases. Those phosphines which conducted double condensation adopted a P,Pchelate mode to form a 6-membered M-P-C-N-C-P to afford cis-MCl2L (M = Pt and Pd). More interesting is the rarely observed P,P-bridging mode exhibited by P{CH2N(R)CH2}2P ligands to form homobimetallic cis-(PtCl2L)2 complexes and {RhCl2(η5 -Cp*)}2L complexes. These metal compounds were obtained and characterised by in situ NMR however their structures were further supported by simulated 31P{1 H} NMR and X-ray studies. Asymmetric Ph2PCH2N(R)CH2P{(CH2)3(NR)2} diphosphines coordinated to Pt(II) in a P,P-chelate fashion affording a mixture of cis and trans bis(chelate) (PtL2)Cl2. Complex in trans geometry was isolated and the structure was further supported by X-ray crystallography. The coordination capabilities of the ligands were investigated with Ru(II) metal centre revealing 'piano-stool' structure of the type RuCl2(η6 -p-cymene)L where the monophosphines adopted a P-monodentate mode and {RuCl2(η6 -p-cymene)}2L where the diphosphines adopted a P,P-bridging mode. Preliminary studies with selected Ru complexes were carried out to investigate their potential catalytic activity to trap CO2 by its insertion into the Ru-Cl bond which suggested that the chloride needs to be substituted by a hydride prior the CO2 insertion. Compounds were characterised by spectroscopic techniques and the structure of some phosphines was further supported by X-ray crystallography.

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