Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: A thorough search through the literature as well as through the Cambridge Crystallographic Structural Database resulted in no examples of a neutral ozone acting as ligand in a complex with any metal. Ionic compounds containing ozonide as anionic species, however, are well known throughout the literature and not surprisingly the only result for 0₃ and a metal in the CCSD was an ionic rubidium ozonide compound. What follows is a systematic study into the result of placing an ozone ligand within complexing distance of a transition metal (the first transition row from titanium to copper). Due to the novelty of the system, as first approximation four different orientations of the ozone ligand relative to the metal (a metal cation in these calculations) were investigated. It was found that coordination through the terminal oxygens resulted in energy minima for all the metal cations, although not necessarily the absolute energy minimum on the potential energy surface for the specific cation. A further structural study was done by adding carbonyl and hydrogen ligands to the system, according to the 18-electron rule. For these calculations coordination through the terminal oxygens was employed. In both series the dissociation energy was also calculated. The dissociation energies for the M(CO)nHm(0₃) complexes were all positive, indicating that they are theoretically stable structures. The resulting wave functions were then analysed with the help of three techniques: Atoms in Molecules (AIM), Charge Decomposition Analysis (CDA) and Natural Bond Orbital Analysis (NBO). AIM showed that bonds were indeed formed between the ozone ligand and the transition metal and hinted that the bonding model can be interpreted with the Dewar-Chatt-Duncanson (DCD) model of σ-donation and л-back donation. CDA confirmed that this was the case. NBO results proved erroneous due to the largely delocalized electronic structure of the complexes. / AFRIKAANSE OPSOMMING: 'n Deeglike soektog deur die literatuur en die Cambridge Crystallographic Structural Database het geen resultate gelewer van komplekse waarin 'n neutrale osoonligand komplekseer met 'n metaal nie. Ioniese verbindings waarin die osonied as anioon optree, is wel bekend deur die literatuur en die enigste resultaat in die CCSD - vir 'n soektog bevattende osoon en 'n metaal - het 'n rubidiumosonied-verbinding opgelewer. Wat volg is 'n stelselmatige studie om die effek te ondersoek indien 'n osoonligand naby genoeg aan 'n oorgangsmetaal geplaas word om kompleksering te bevoordeel (metale wat gebruik is, is die eerste oorgangsreeks vanaf titanium tot koper). As gevolg van die onbekendheid van die sisteem is vier verskillende oriëntasies van die osoonligand relatied tot die metal ('n metal katioon in die geval) as beginpunt ondersoek. Daar is gevind dat koordinasie deur die terminale suurstowwe van die osoonligand vir al die metal katione lei tot energie minima, alhoewel dié minima nie noodwendig die globale minima op die potensiële energie oppervlaktes van die katione is nie. 'n Verdere studie is gedoen deur karboniel- en waterstofligande tot die sisteem te voeg, gelei deur die 18-elektron reel. Vir hierdie berekeninge is koördinasie deur die terminale suurstowwe gebruik. In beide reeks is dissosiasie-energieë bereken. Die dissosiasie energieë van die M(CO)nHm(0₃) komplekse was deurgaan positief wat aandui dat die komplekse teoreties stabiel is. Die verkrygde golffunksies is hierna analiseer deur middel van drie tegnieke: Atoms in Molecules (AIM), Charge Decomposition Analysis (CDA) en Natural Bond Orbital Analysis (NBO). AIM het getoon dat bindings inderdaad gevorm word tussen die osoonligand en die metal en bet die moontlikheid laat ontstaan dat die bindingsmodel volgens die Dewar-Chatt-Duncason (DCD) model van σ-donasie en л-terugdonasie geïnterpreteer kan word. Hierdie waarneming is bevestig deur CDA. NBO resultate kon nie suksesvol gebruik word nie as gevolg van die hoë graad van electron delokalisasie van die komplekse.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Modification of chitosan with benzoylisothiocyanate was attempted, however due to solvent problem the study was left incomplete till appropriate solvent is designed. N,N-diethyl-N -camphanoylthiourea (HL8), N-piperidyl-N '-camphanoylthiourea (HL9), N-pyrrolidyl-N -camphanoylthiourea (HL10) and N,N-diethyl-N -adamantylcarbonyl thiourea (HL11)have been synthesised and characterised for the first time. Two of these ligands HL8 and HL11, were used to form a number of transition metal complexes, namely H30+{fae-[Co(L8-S,Obn, cis-[Ni(L8-S,0)2], trans-[Cu(L8-S,0)2], translcis-[Zn(L 8_S,0)2], translcis-[Pt(L 8_S,0)2], Ag2[(HL8-S)(L-J.1-S,O)]2, translcis- [Ni(L11-S,O)2]and translcis-[Cu(L11_S,O)2]. The new products are fully characterised by means of MS, IR spectroscopy, NMR spectroscopy, elemental (C, H, Nand S) analysis and melting point determinations. The H30+{fae-[Co(L8-S,Obn, cis-[Ni(L8- S,O)2], trans-[Cu(L8-S,O)2] and Ag2[(HL8-S)(L-J.1-S,O)]2 are also characterised by Xray diffraction analysis. The structure of the new chiral N,N-dialkyl-N' -camphanoylthiourea ligand (HL8) has a significant effect on its coordination chemistry with transition metal ions. This ligand forms H30+ {fae-[Co(L8-S,Obn, cis-[Ni(L8-S,0)2], trans-[Cu(L-S,O)2] and Ag2[(HL8- S)(L8-J.1-S,O)]2 complexes with the Co(II), Ni(II), Cu(II) and Ag(I) metal ions respectively. The spectroscopic and X-ray diffraction results of these complexes indicate a bidentate mode of coordination of the ligand (with its Sand °donor atoms) to the Co(II), Ni(II) and Cu(II) metal ions. The reaction of this ligand with silver(I) however affords the formation of a binuclear silver(I) complex exhibiting monodentate and bidentate modes of coordination within the same complex. The exclusive formation of trans-[Cu(L8-S,0)2] is a new phenomenon for the HL type thiourea ligands with Sand °donor atoms. Up to this point a maximum of 15 % trans-isomer has been reported in ltterature." All the transition metal complexes made with HL8and HL11are air stable in both the liquid and solid states except the H30+{fae-[Co(L 8-S,Ob]} Interestingly the deep green fae- H30+{fae-[Co(L8-S,Obn complex is air sensitive and the Co(II) oxidizes to Co(III) in the complex by atmospheric O2. The oxidation of Co(II) to Co(III) in the complex is confirmed by 1Hand 13CNMR spectra as well as by UV-Visible spectra of the complex. The NMR spectra of the complexes indicated the presence of one isomer in each complex except for the NMR spectra of the platinum complex of the HL8 ligand. The presence of the minor trans-[Pt(L8-S,Q)21 isomer in combination with the major cis-[Pt(L8-S,Q)21 isomer in the platinum complex was indicated by the 1H, 13Cand 195ptNMR spectra of the complex. / AFRIKAANSE OPSOMMING: Pogings om chitosan met benzoylisothiocyanate te modifiseer is onvoltooid gelaat weens die gebrek aan'n geskikte oplosmiddel. N,N-diethyl-N -carnphanoylthiourea (HL8), N-piperidyl-N -camphanoylthiourea (HL9), N-pyrrolidyl-N -camphanoylthlourea (HL10) en N,N-diethyl-N -adamantylcarbonyl thiourea (HL11) is vir die eerste keer gesintetiseer en gekarakteriseer. Twee van die ligande, HL8 en HL11, is gebruik om verskeie oorgangsmetaalkomplekse te berei, nl. H30+{fac-[Co(L8-S,Ohn, cis-[Ni(L8-S,0)2], trans-[Cu(L8-S,0)2], trans/cis-[Zn(L8 - S,0)2], trans/cis-[Pt(L8-S,0)2], Ag2[(HLB-S)(L-jl-S,0)]2, trans/cis-[Ni(L11-S,0)2] en trans/cis-[Cu(L11_S,0)2]. Die nuwe produkte is volledig gekarakteriseer deur middel van MS, IR spektroskopie, KMR spektrometrie, elemente (C, H, N en S) analise en smeltpuntbepaling. Die komplekse H30+{fao-[Co(L8-S,0)3n, cis-[Ni(L8-S,0)2], trans- [Cu(L8-S,0)2] en Ag2[(HLB-S)(L-jl-S,0)]2 is ook deur middel van X-straaldiffraksieanalise gekarakteriseer. Die struktuur van die nuwe chirale N,N-dialkyl-N'-camphanoylthiourea ligand (HL8) het In beduidende invloed op die koordinasie van hierdie ligand met oorgangsmetaalione. Die ligand vorm H30+{fac-[Co(L8-S,Ohn, cis-[Ni(L8-S,0)2], trans-[Cu(L-S,0)2] en Ag2[(HL8-S)(L8-Il-S,0)]2 komplekse met Co(ll)-, Ni(II)-, Cu(II)- en Ag(I)-ione respektiewelik. Spektroskopiese en X-straaldiffraksie-analise van die komplekse toon dat die ligande op 'n bidentate wyse d.m.v. die S- en O-donoratome met Co(II), Ni(lI) en Cu(lI) koordineer. Die reaksie van hierdie ligand met Ag(I)-ione lei egter tot die vorming van 'n dikernige silwer(I)-kompleks waarin die ligande monodentaat (S) en bidentaat (S en 0) aan die metaal gebind is. Die vorming van uitsluitlik die trans-[Cu(L8-S,0)2] in die reaksie van HL8 met Cu(lI) is 'n besondere fenomeen in die chemie van hierdie tipe ligande; in die literatuur word melding gemaak van slegs een ander trans-kompleks met hierdie ligande, en dan wel met 'n maksimum opbrengs van 15%.29 Alle oorgangsmetaalkomplekse met HLB en HL11 is stabiel indien blootgestel aan lug, ongeag of die verbindings opgelos word of in die vastetoestand verkeer, behalwe H30+{fao-[Co(L8-S,Ohn. Die diep-groen gekleurde H30+{fao-[Co(L8-S,Ohn)3]} kompleks is lugsensitief; Co(lI) word deur lugsuurstof na Co(lIl) ge-oksideer. Die oksidasie in die kompleks kan deur middel van 1H en 13CKMR spektrometrie sowel as UV-sigbare spektrofotometrie bevestig word. Die KMR spektra van alle komplekse dui op die teenwoordigheid van slegs een isomeer in oplossing, behalwe in die geval van die platinum(lI) kompleks met HL8. Die teenwoordigheid van lae konsentrasies trans-[Pt(L8-S,0)2] isomeer tesame met veel hoër konsentrasies van die cis-[Pt(L8 -S,O)2] isomeer word deur 1H, 13Cen 195ptKMR spektroskopie aangedui.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

No description available.

Although known since the 1930s, organogold chemistry has been dormant until recently, primarily due to preconceptions about the inertness of gold in transformations. However, this last decade has witnessed the emergence of a Golden Age with the development of a wealth of reports on gold in a plethora of reactions. In recent years, the drive for more atom- and step-economical and environmentally friendly reactions has become a field of intense research. In our on-going research on well-defined transition metal complexes bearing NHC ligands, our group recently discovered a new gold(I) hydroxide complex [Au(OH)(IPr)] (1a) that can be easily synthesised from the chloride precursor [AuCl(IPr)] (1b). A preliminary survey of the reactivity of this gold synthon has demonstrated interesting reactivity that holds great potential in bond activation reactions and the development of useful synthetic methods. Simplistically, this gold hydroxide complex can be seen as a strong Brønsted base. This thesis is dedicated to an in-depth examination of the reactivity of this complex in base-free bond activation reactions. Two themes predominate in the following chapters: the first part demonstrates the activity of gold(I) hydroxide as a bond activation agent to readily and efficiently access organogold complexes while the second part studies the reactivity of this compound in decarboxylation processes with carboxylic acids. Chapter 2 and 3 were dedicated to the development of new synthetic routes to access organogold complexes via base-free transmetalation reactions with organoborons and silanes using 1a. The combination of experimental and computational studies allowed identification and isolation of key intermediates in these reactions. Chapter 4 can be seen as a transition between the development of novel methodologies to synthesise aryl and heteroarylgold complexes and the first steps of gold hydroxide 1a as mediator in decarboxylation reaction. As a result, a novel mode of reactivity for gold was discovered and the synthetic route developed constitutes one of the greenest procedures to prepare organogold complexes with the generation of water and CO₂ as only side products. Chapter 5 and 6 venture further into the exploration of 1a in decarboxylation reactions and detail the development of a catalytic process for the protodecarboxylation reaction and subsequent mechanistic investigations of this reaction through stoichiometric experiments and kinetic and computational studies.

Ph.D. / Chapter 1 presents a brief overview on the development of platinum, ruthenium and gold anti-cancer complexes. The clinical success of cisplatin has been a tremendous impetus for the design of metal-based antitumor drugs. Its mechanism of action is therefore briefly discussed, as well as the toxic side effects of its clinical use and the cellular resistance to the drug. It is its side effects and drug resistance that have stimulated the development of cisplatin analogues and other metal based anti-cancer agents. Compounds showing most promise are ruthenium complexes which are structurally different but have the same stability and show similar modes of binding to DNA. The last part of the introduction deals with the development of gold(I) and gold(III) complexes, the main topics of the research described in this thesis. Chapter 2 reports on the attempted preparation of dppf and dippf gold(III) complexes. However, the reaction of these diphosphines with H[AuCl4] and Na[AuCl4] all led to isolation of gold(I) complexes (dppf)Au2X2 (X = Cl (1), Br (3)) and (dippf)Au2X2 (X = Cl (2), Br (4)). In an attempt to oxidize the gold(I) complexes, (dppf)Au2Br2 (3) and (dippf)Au2Br2 (4) were reacted with excess bromine yielding two new complexes (C5H4Br3)(PR2)AuBr (R = Ph, 5; R = i-Pr, 6). This bromination reaction could be extended to the ligands and bromination of the free diphosphinoferrocene ligands produced the expected brominated cyclopentenes (C5H4Br3)(PR2) (R = Ph, 7; R = i-Pr, 8) in good yields. However, these could not be complexed to gold due to reduced basicity of 7 and 8. When the bromination was performed under wet aerobic conditions the oxidized pseudo-centrosymmetric product, [doppf][FeBr4] (9) {doppf = 1,1’-bis(oxodiphenylphosphino)ferrocene, was obtained as the major product. Solid-state structures of 1, 2, 4, 6, and 9 were established by means of single-crystal X-ray crystallography. Chapter 3 reports on the use of chiral Josiphos and Walphos diphosphine ligands to form palladium, platinum and gold complexes. The platinum complexes were prepared by reacting the ligands with [PtCl2(cod)] while the palladium complexes were prepared from [PdCl2(NCMe)2]. The complexes obtained had the general formula [MCl2(P-P)], where M = Pd, Pt, and P-P = Josiphos or Walphos ligand, and were obtained in good yields. The X-ray structures of a palladium(II) and a platinum(II) complex of the same Josiphos ligand were determined. The Josiphos complexes 12 and 14 show good solubility in common solvents. Furthermore, the complexes remained soluble and stable in a 40:60 water:DMSO mixture. The Walphos complexes 13 and 15 rapidly precipitated under the same conditions. In line with this limited solubility 13 and 15 showed minimal cytotoxic effects when compared to their Josiphos counterparts 12 and 14 whose cytotoxic effects (in terms of IC50 values ) were six to seven times less than cisplatin. Reaction of the Walphos ligand and H[AuCl4] in a 1:1 ratio gave a dinuclear gold(I) complex 18 while the same reaction with Josiphos gave a mixture of intractable materials. However a 1:1 reaction of the Josiphos with AuCl(tht) gave a mononuclear three-coordinate gold(I) complex 16. A P^N chiral ligand comprising of a diphenylphosphine and a pyrazole moiety was also prepared and was complexed with AuCl(tht) to give a phosphine bound gold(I) complex 19. The structure of this complex was determined by X-ray studies. From the studies it became evident that apart from increasing the basicity of compound the pyrazolyl moiety remains dangling and the complex shows bond parameters similar to those observed with monophosphine ferrocenyl complexes. Chapter 4 reports on the bidentate and monodentate gold(III) complexes based on the (pyrazolylmethyl)pyridine ligands together with their platinum(II) complexes. The denticity of the complexes depended on the position of the pyrazolyl moiety relative to the pyridine nitrogen. When ortho-substituted ligands were reacted in a 1:1 ratio with H[AuCl4] in a mixture of water and ethanol at room temperature, bidentate cationic complexes of the general formula [AuCl2(PyCH2R2pz)][X], where R = Me (20), X = AuCl4-; R = Ph (21), X = Cl-; t-Bu (22), X= Cl- and p-tol (23), X = AuCl4-, were obtained. When para-substituted ligands were used under same reaction conditions, neutral monodentate complexes [AuCl3(PyCH2R2pz)], where R = Me (24) and R = Ph (25), were obtained. Platinum(II) complexes were obtained using K2[PtCl4] in a mixture of water and ethanol under reflux, and affords neutral complexes of the type [PtCl2(PyCH2R2pz)], where R = Me (27), Ph (28), t-Bu (29) and p-tol (30). When acetone was used instead of ethanol monoacetonylplatinum(II) complex (29a) was formed and on prolonged heating formation of the diacetonyl complex (28b) was observed. Both the platinum and the gold complexes were evaluated for their anti-cancer potency. The gold(III) complexes were devoid of any activity while the platinum complex 30 showed activity 8 times lower than cisplatin. The structures of 23, 25, 28, 29 and 29a were determined from single-crystal X-ray diffraction studies. In Chapter 5, tridentate complexes based on bis(pyrazolylethyl)amine are reported. These were prepared with the aim of improving water-solubility and cytotoxicity of the resulting complexes. New synthetic methods for preparation of the ligands NH(CH2CH2pz)2 (R = Me (L7), H (L8), t-Bu (L9)) under mild reaction conditions were developed albeit the yields obtained were generally low. The reaction of these ligands with H[AuCl4] gave corresponding tridentate dicationic gold(III) complexes [NH(CH2CH2pz)2][X]2 (R = Me (31), H (32), X = AuCl4 , and R = t-Bu (33), X = Cl-). Despite the ligands stabilizing the gold(III) ion, they showed no solubility in water. In an attempt to make the ligand system water soluble, a thiocarbamate analogue with pyrazolyl groups replaced by hydroxyl groups was prepared. However the resulting gold(III) complex [Au{CS2N(CH2CH2OH)2}2][AuCl2] (34) was found to be only soluble in DMSO.

Please refer to full text to view abstract / Prof. A. Roodt

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