Chemistry

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Browsing Chemistry by Advisor "Conradie, Jeanet"

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    Quantum computational, structural and electrochemical properties of substituted dithizones and photochromic dithizonato phenylmercury complexes
    (University of the Free State, 2010) Botha, Ebrahiem; Von Eschwege, Karel Grobler; Conradie, Jeanet
    English: For the purpose of investigating the influence on the photochromic reaction of its phenylmercury complexes, a series of dithizone derivatives were at first synthesized. This includes symmetrical dithizone derivatives with electron-donating ability; ortho, meta & para-methyl and methoxy, as well as the 3,4-dimethyl derivative, including some of its disulphide and dehydrodithizone oxidation products. The synthesis of extended aromatic ring dithizone derivatives was attempted, i.e. instead of a phenyl ring the dithizone was extended to have napthyl, fluorenyl, anthracenyl and pyrenyl functional groups. Synthetic procedures were optimized, while conveniently utilizing ammoniumsulphide instead of NH3(g) and H2S(g) as reagent. Phenylmercury(II) complexes were prepared from the successfully synthesized ortho and meta-methoxy, and ortho, meta and para-methyl, and napthyldithizone derivatives. All except the ortho-methyl and naphthyl dithizonates were observed to be photochromic. The ortho-methoxy dithizonate, for the first time, exhibited an alternative color reaction; instead of the usual orange to blue, this compound changed from pink to purple. From the corresponding substituted dithizone the disulphide of ortho-fluorodithizone was synthesized through auto-oxidation, chemical oxidation and electrochemical oxidation. Successful growth of a sizeable crystal of the latter compound ended in solving, for the first time, the X-ray crystal structure of a dithizone disulphide, giving conclusive evidence in support of the long standing proposal of an unstable disulphide intermediate in the oxidation reaction of dithizone. Solving also the X-ray crystal structure of ortho-methoxydehydrodithizone gave indirect structural evidence in support of the foregoing synthesis product. A comprehensive ADF DFT quantum computational study included the successfully and unsuccessfully prepared dithizones and dithizonatophenylmercury complexes. Results unambiguously showed the symmetric form of dithizone and its analogues to be the most stable. TDDFT calculations simulate the trends seen in experimental UV/visible spectra. Graphical representations show molecular orbitals (HOMO & LUMO) extending over the entire length of the ligand, confirming the molecule’s structural importance in the photochromic reaction. Extended dithizonates pose a steric hindrance for photochromism to take place. Electrochemical studies were performed on the above successfully synthesized ligands and complexes, as well as some fluoro-substituted dithizones, exploring the electronic borders within which photochromism ultimately takes place. Complete redox schemes are proposed for the observable redox waves in the cyclic voltammograms of all species involved. An approximate linear relation between experimental oxidation data of the dithizonates and the calculated HOMO energies was found (R2 = 0.89).
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    Synthesis, chemical kinetics, thermodynamic and structural properties of phenyl-containing beta-diketonato complexes of rhodium (I)
    (University of the Free State, 2007) Stuurman, Nomampondomise Flaurette; Conradie, Jeanet
    Rhodium compounds are one of the most widely used industrial homogeneous catalysts for organic raw material processing. Classic examples of efficacious catalyst systems are: methanol carbonylation to give acetic acid in the presence of [Rh(C0)₂I₂] complex (Monsanto prosess),¹ alkene hydroformylation on RhHCO(PPh₃)₂ catalyst, hydrogenation of olefins and acetylenes with the help of RhCl(PPh₃)₃ (Wilkinson's catalyst)² and the use of [Rh(acac)(CO)i]₂ in the hydroformylation of olefins³ (Figure 1.1). In the field of olefin polymerization, metal complexes with a coordinatively unsaturated Lewis acid metal centre are generally required, whereas for transformations such as the carbonylation of methanol, electron-rich metal centres are necessary to favour oxidative addition of Mel to Rh(I).⁴ ⁵ The high catalytic reactivity of these rhodium complexes is in many respects due to the nature of ligand surroundings.⁶ Supported rhodium carbonyl complexes form an important class of catalysts and precursors for the preparation of different supported rhodium species.⁷ The reactivity of rhodium(I) dicarbonyl complexes, and in particular, the rate of carbonyl ligand substitution, is defined by the electron state of the rhodium centre.⁶ The latter ultimately depends on donor-acceptor characteristics of chelated ligand atoms coordinated directly with the metallic centre.⁶ Kinetic and thermodynamic studies on the octahedral rhodium(III) complexes has gained momentum. This field has also given rise to the important discovery of the photosensitivity of rhodium complexes. β-diketone complexes of Rh(I) of the type [Rh(β-diketone)(D)₂ (where D are electron donors such as CO, ethylene and dienes) undergo substitution reactions with a large variety of ligands. To examine these reactions, knowledge of the relative 𝘵𝘳𝘢𝘯𝘴-effect of these ligands is necessary. The unexpected discovery of the antitumor activity of cisplatin has opened up the 'era of inorganic cytostatics' .⁹ In the search for new organometallic compounds or inorganic coordination complexes with antitumor properties, it was found that some rhodium(!) complexes, for example [Rh(acac)(cod)] (acetylacetonate- I ,5-cyclooctadienerhodium(I)), showed antineoplastic activity comparable to, or even better than that of 𝘤𝘪𝘴𝘱𝘭𝘢𝘵𝘪𝘯. ¹º ¹¹