Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, March 2003. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references. Also available in electronic version.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references. Also available in electronic version.

Photocatalytic reactions of tin diphthalocyanine, Sn ^IVPc₂ and anionic form of Nd^III, Dy^III, Eu^III, Tm^III and Lu^III diphthalocyanine complexes ( [Pc(-2)Nd^IIIpc(-2)]⁻ , [Pc(-2)Dy^IIIPc(-2)]⁻ , [Pc(-2)Eu^IIIPc(-2)⁻, [Pc(-2)Tm^IIlPc(-2)r and [Pc(-2)LuIIIpc(-2)]⁻ respectively) in the presence of CH₂CI₂, S0₂, pentachlorophenol (PCP), 4-chlorophenol (4-Cp) and thionyl chloride have been studied. Photoreactions involving lanthanide diphthalocyanines, filtered and unfiltered radiations were employed, whereas for photoreactions involving tin diphthalocyanine, only unfiltered radiation was employed. For lanthanide diphthalocyanine complexes, LnPce-, the photosensitization power increases with the decrease of the lanthanide ionic radii, implying that the photocatalytic activity of LnPc₂⁻ complexes is associated with the π-π interaction between both phthalocyanine rings. Thus, LuPc₂⁻ is a better photocatalyst than other lanthanide diphthalocyanine complexes. Photolysis ofSnPc₂ in an acetonitrile/dichloromethane solvent mixture, using unfiltered radiation from a tungsten lamp, results in the one-electron oxidation of this species to [Pc( -2 )Sn(IV)Pc(-1)]⁻. The relative quantum yields for the disappearance of SnPc₂ are in the order of 10⁻¹. The photoreaction of SnPc₂ is preceded by excitation to nπ* excited states, before been ,quenched by CH₂CI₂. The one-electron oxidation species, [Pc(-2)Sn(lV)pc(-1)]⁻ was also formed during the photolysis of SnPc₂ in dichloromethane containing S0₂, and with quantum yields of order of 10⁻³. Visible photolysis of [Pc( -2)Nd^IIIpc(-2)]⁻, [Pc(-2)Dy^IIIPc(-2)]⁻ and [Pc(-2)Lu^IIIpc(-2)]⁻ in N,N. dimethylformamide (DMF)/dichloromethane solvent mixture containing SO₂, results in the formation of the one-electron oxidation species, Pc(-2 )Nd^IIIpc(-1), Pc( -2) Dyi^IIIPc(-1) and Pc(-2)Lu^IIIpc(-1), respectively. The relative quantum yields are in the order of 10². The photoreactions are preceded by population of the excited triplet state,³π-π* [ LnPc₂]⁻ complex, before exchanging an electron with S0₂. The one-electron oxidation species of Dy^III and Lu^III diphthalocyanine complexes have also been formed from visible photolysis of [Pc(-2 )Dy^IIIPc(-2)]⁻and [Pc(-2)Lu^IIIpc(-2)]⁻in acetonitrile containing PCP. The PCP is reductively dechlorinated to tetra- and trichlorophenols. The quantum yields for the photosensitization reactions are in the order of 1 0⁻. Photolysis, using visible radiation from 220 W Quartzline lamp, of an aqueous solution of 4-Cp, saturated with oxygen and containing a suspension of solid [Pc(-2)Nd^IIIpc(-2)]⁻, results in the formation of benzoquinone, hydro quinone and 4-chlorocatechol. The quantum yields for the degradation of 4-Cp are in the order of 10⁻. Langmuir-Hinshelwood kinetic model shows the adsorption of 4-chlorophenol onto solid [Pc(-2)Nd^IIIpc(-2)]⁻. Lanthanide diphthalocyanine complexes ([Pc-2)Nd^IIIpc(-2)]⁻. [Pc(-2)Eu^IIIpc(-2)]⁻, (Pc(-2)Tm^IIIpc( -2)]⁻ and (Pc(-2)Lu^IIIpc(-2)]⁻) undergo one or two-electron oxidation in the presence of thionyl chloride. At low concentrations of SOCI₂(<10⁻⁴ mol dm⁻³) the visible yhotolysis of [Pc(-2 )LnPc(-2)]⁻ complexes result in the one-electron oxidation, giving neutral lanthanide diphthalocyanine species, Pc(-2)Ln^IIIpc(-1). The Pc(-2 )LnPc(-I) species undergoes one-electron photooxidation to [Pc(-I )LnPc( -I)]⁻ in dichloromethane and in the presence of SOC₁₂. At large concentrations of SOC₁₂ (>10⁻² mol dm⁻³), direct two-electron oxidation of the (Pc(-2 )LnPc - 2)]⁻ species to (Pc(-1)LnPc(-1)]⁻ occurs. Spectroelectrochemical behaviours of Sn^IVPc₂ have been also studied. The cyclic voltammetry ofSnPc₂ in CH₂CI₂/TBAP show two reduction couples at -0.56 V and -0.89 V versus saturated calomel electrode (SCE) and one oxidation couple at 0.35 V versus SCE. In DMFITEAP system, the reduction couples are observed at -0.44 V and -0.81 V versus SCE whereas the oxidation couple occurred at 0.43 V versus SCE. The oxidation couple corresponds to [Pc(-2 )Sn^IVPc(-2 )]/[Pc(-2)Sn^IVPc( -I)] . and the reduction couples to [Pc(-2)Sn^IVPc( -2 )]/[Pc(-2 )Sn^IVPc( -3 )]⁻ and [Pc(-2)Snl^IVPc( -3)] ⁻/[Pc(-3 )Sn^IVPc(-3)]²⁻, respectively. The electronic absorption spectra of these reduced and oxidized species are reported.

A new synthetic route to cyclophanenes 56, starting from an appropriate 2,6-dihalogen-substituted toluene via monothiacyclophanes as intermediate compounds, was developed. By this method, anti-5,8,13-16-tetramethyl [2,2] (1,3)cyclophan-1-ene, 56b, and anti-4,6,8,12,14,16-hexa-methyl [2,2] (1,3)cyclophan-1-ene, 56c, were first synthesized as well as three new monothiacyclophanes, anti-9,17-dimethyl-2-thia [3,2] (1,3) cyclophane, 72a, anti-6,9,14,17-tetramethyl-2-thia [3,2] (1,3) cyclophane, 72b, anti-5,7,9,13,15,17-hexamethyl-2-thia [3,2] (1,3) cyclophane, 72c. An X-ray structural determination of the monothiacyclophane 72a revealed an anti-stepped geometry of the molecule and that the aromatic rings were bent outward in a slightly distorted boat form. A reciprocal relationship between deviations of the inner carbons from their basal planes and distances between the inner carbons was found by comparison of X-ray data of four metacyclophanes. Several tricarbonylchromium(0) and η5-cyclopentadienyl-iron(I) complexes of cyclophanenes 56 were also prepared for the first time. The complexation effect and ring current reduction effects in these complexes were investigated through studies of their proton nmr spectra. An X-ray structure analysis of anti-8,16-dimethyl [2,2] (1,3) cyclophan-1-ene-cyclopentadienyliron(I), 105a, was determined and it was found that the bridge double bond (1.345A) has a cis geometry but with very large torsional angles: 24.7° for C-C=C-C and 41.6° for H-C=C-H. The bridge chemistry of cyclophanenes 56 and their metal complexes was investigated through some selected reactions. It was found that the cyclophanenes 56 were easily oxidized in attempted electrophilic additions to the bridge double bond. Bromination of the cyclophanene-iron complexes 105b and 105c did give the desired bromine adducts. However, it was found that the reactivity of the bridge double bond in cyclophanenes 56 is very low since most of the attempted reactions failed to give the desired products. The first synthesis of the (η6, η6-anti-4,6,8-trimethyl [2,2] (1,3) cyclophan-1,9-diene)-bis(tricarbonylchromium(0)), 133, was achieved through the dithiacyclophane route. An X-ray structure analysis of 133 was also determined and found that the two aromatic rings were inclined at 19.8° with respect to each other. / Graduate

The ligands of the ten-membered series, [10]-aneS3, [10]- aneS2N, [10]-aneSN2 and the macrobicyclic ligand - 1,4-bis(1-aza- 4,8-dithia-4-cyclodecyl) ethane, and their transition metal complexes were successfully synthesised. Chromium (III) complexes of the homoleptic hexaaza ligands [18]-aneN6 and [20]-aneN6 were synthesised, structurally characterised and their spectral properties studied. Bis complexes of Ni(II) with [10]-aneS3, [10]-aneS2N and [10]-aneSN2 were octahedral as is evident from their crystal structures. The esr spectra of the corresponding Ni(III) complexes are characteristic of a low spin d7 ion in a compressed octahedral coordination in the complex based on [10]-aneS2N and an elongated octahedral coordination in the complexes based on [10]-aneSN2 and [10]-aneS3. The spectral and electrochemical properties of the various Ni(II) complexes are compared with each other. The redox reactivity of the Ni(II) complex based on [10]-aneS3 was studied. The synthesis of a macrobicyclic ligand is described. The Ni(II)complex of the macrobicyclic ligand is a distorted octahedron and the esr spectrum of the Ni(III) complex is characteristic of a low spin d7 ion in a compressed geometry. The covalency parameter K, and the energy separation between the low spin ground state and the first excited high spin state were determined from the esr and the electronic spectra of the Ni(III) complex. Two isomers for the Pd(II) bis complexes of [10]-aneS2N were obtained and characterised by X-ray methods and nmr spectroscopy. Evidence for the formation of a high spin Pd(II) octahedral species has been provided for the first time. Oxidation of the Pd(II) complex is metal centered and the esr spectra of the Pd(III) complexes are characteristic of a low spin d7 PdS4N2 core. Fe(II), Fe (III), Co(II), Co(III), Ni (II) and Pd(ll) bis complexes of the ligand [10]-aneS3 were synthesised and characterised by elemental analysis, nmr and esr spectroscopies, where appropriate, and their spectral and electrochemical properties studied. The crystal structures of Fe(II), Co (II) and Ni(II) bis complexes of [10]-aneS3 were octahedral with three S atoms from each of the thioether ligands coordinated to the central metal ion. The esr spectra of the Fe(III) bis complexes of [9]-aneS3 and [10]-aneS3 were characteristic of a low spin d5 complex ion. The ligand field distortion parameters were obtained from the electronic and esr spectra and the energies of the Jahn-Teller splitting were estimated. The Co(II, bis complex of [10]-aneS3 is low spin. The half-wave potentials due to the [special characters omitted] and [special characters omitted] couples were obtained by cyclic voltammetry. The electron self exchange rate constant for the [special characters omitted] and the [special characters omitted] couples were determined by the 59Co nmr line broadening technique for the first time. The self exchange rate constant for the [special characters omitted] couple was determined by the 'H nmr line broadening technique. The crystal structure of the Pd(II) bis complex of [10]—aneS3 is essentially square planar with significant interactions from the axial S atoms. This complex is fluxional as is evidenced in the variable temperature nmr spectra. / Graduate

M.Sc. / The aim of this project was the synthesis of viridamine analogues, to be used for selective metal complexation. This, therefore, required the synthesis of diketopiperazines, containing an imidazole-type side chain. The imidazole functionality was introduced into the synthesis via peptide acid coupling reaction between histidine and another amino acid. Before any coupling reactions were possible it was necessary to protect the carboxylic acid functionality of one of the two amino acids being used and the amine functionality of the other. This was to prevent mixed products forming. Owing to the continued difficulty at achieving selective N-protection of histidine, it was decided to make use of the corresponding methyl ester instead. After some initial attempts, it was found that the methyl ester of histidine, which was bought as the dihydrochloride salt, could be readily coupled to a variety of Boc protected amino acids. The Boc protected amino acids could be prepared under various conditions using di-tertbutyl dicarbonate. A range of conditions was investigated for the coupling of the two amino acids, i.e. the histidine methyl ester dihydrochloride and a Boc protected amino acid. Successful coupling was finally achieved using tetrahydrofuran as solvent, N-hydroxy benzotriazole as reaction promoter, N-methyl morpholine as a base and dicyclohexylcarbodiimide as the coupling agent. After varying the reaction conditions the optimised reaction conditions gave yields in the region of 76%. Once coupling had been achieved, it remained to cyclise the dipeptide. Cyclisation was preceded by the removal of the Boc protecting group either in situ or in a two step process. In the absence of the imidazole functionality, removal of the Boc group was readily achieved using trifluoroacetic acid. However, attempted deprotection of dipeptides containing the imidazole functionality led to decomposition of the dipeptide under identical conditions. It was therefore necessary to find an alternative form of deprotection. This was found in the form of formic acid, which proved to be successful in removing the Boc group and in effecting cyclisation to the analogous diketopiperazine. This particular form of in situ cyclisation proved to be very low yielding. This problem was circumvented by following the formic acid treatment by a period of reflux in a toluene I 2-butanol mixture. Cyclisation was effected with pure products being obtained in high yield, after column chromatography. Complexation reactions were initiated with the synthesised diketopiperazines but unfortunately no X-Ray diffraction studies could be carried out, due to the formation of amorphous solids instead of crystalline materials.

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Please read the abstract in the section 00front of this document / Thesis (PhD (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted