The butyne, HC≡CCF(CF₃)₂, can be prepared via the dehydro-halogenation of ICH=CHCF(CF₃)₂, the olefin is produced by the ultraviolet irradiation of mixtures of (CF₃)₂CFI and acetylene. Group IV perfluoroalkynyl derivatives (CH₃)[subscript n]M(C≡CR[subscript f])[subscript 4-n] (n = 0 ↦ 3; M = Si, Ge, Sn; R[subscript f] = CF₃> C₂F₅, CF(CF₃)₂) can be prepared by the reaction of XMg C≡CR[subscript f] (X = Br, I) with the appropriate group IV organohalide. Some, but not all, of the combinations of n, M, and R[subscript f] are described. The reaction of CH₃Si[symbol omitted]₃ with IMgC≡CCF₃ produces (CH₃)₂Si(C≡CCF₃)₂. Difluorocarbene from (CH₃)₃SnCF₃ at 150° adds to the C≡C bond of HC≡CR[subscript f] (R[subscript f] = CF₃, C₂F₅, CF(CF₃)₂) and some of the (CH₃)[subscript n]M(C≡CR[subscript f])[subscript 4-n] derivatives to give the corresponding cyclopropenes, [formula omitted] and [formula omitted] respectively. The spectral properties of the group IV perfluoroalkynyl and cyclopropenyl derivatives exhibit several novel trends. The difluorocarbene species from (CH₃)₃SnCF₃ is electrophilic and is in a singlet state in gas phase addition reactions to unsaturated bonds. The carbene adds stereospecifically to both cis- and to trans-butene-2 to give the corresponding isomeric cyclopropanes. The carbene also inserts into the Sn-H bond of (CH₃)₃SnH. The ultraviolet irradiation of mixtures of (CF₃)₂CFI and (CH₃)₃SnSn(CH₃) produces (CH₃) ₃SnCF(CF₃) ₂. A similar reaction involving (CH₃)₃SnSn(CH₃)₃ and CF₂=CFI produces (CH₃)₃SnCF=CF₂. None of the derivatives, (CH₃)₃SnR[subscript f] (R[subscript f] = C₂F₅, CF(CF₃)₂, CF=CF₂) , produces a carbene upon pyrolysis. Bis(trifluoromethyl)diazomethane reacts with HC≡CCF₃ and with CF₃C≡CCF₃ at ca. 150° to give a mixture of the corresponding isopyrazole, [formula omitted], and cyclopropene, [formula omitted]. Similar reactions of the diazo compound with (CH₃)₃MC≡CCF₃ (M = Ge, Sn) produce [formula omitted] derivatives. The reaction of bis(trifluoromethyl)diazirine and (CH₃)₃GeC=CCF₃ also produces the cyclopropene. The diazo compound inserts C(CF₃)₂ into the M-H bonds of (CH₃)₃SnH and (CH₃)₂AsH and produces (CH₃ )₂AsCF(CF₃) ₂H and (CH₃)₂AsCF=CF₂ upon reaction with (CH₃)₂AsAs(CH₃)₂. The diazo compound fails to react however, with either (CH₃)₃MH (M = Si, Ge), (CH₃)₃GeBr, or (CH₃)₃ GeGe(CH₃ )₃. The Mössbauer spectra of the compounds (CH₃)₃SnR[subscript f] reveal that the quadrupole splitting in the Sn nucleus increases in the order R[subscript f] = CFH₂ < CF₂H < CF₃ ≲ CH(CF₃)₂ < C₂F₅ < CF(CF₃)₂ which indicates the order of increasing electronegativity of the R[subscript f] groups. The order of electronegativity, CF₃ < C₂F₃ < CF(CF₃)₂, is also supported by n.m.r. studies of the compounds HC≡CR[subscript f] and [formula omitted]. As an Appendix the stereochemistry of the olefins produced by the ultraviolet irradiation of mixtures of R[subscript f]I (R[subscript f] = CF₃, C₂F₅, CF(CF₃)₂) and acetylene is described. Predominantly trans addition takes place. / Science, Faculty of / Chemistry, Department of / Graduate

The chemoselective hydrozirconation reaction of a series of 1-ene-3-yne molecules 51a-d, using the commercially available hydride reagent, Cp₂ZrCl(H) 1, provides an efficient route to the syntheses of 1,3-dienes 55a-d, substituted at the 1-position by the Cp₂ZrCl moiety. Similar chemoselectivity was observed in the hydrozirconation reaction of α, β-unsaturated nitriles, to generate the corresponding 1-azadienyl complexes 68-71. The complexes 55a-d were found to be useful general precursors in the preparation of other heterosubstituted 1,3-dienes. Thus, corresponding tin-, phosphorus-, boron-, selenium-and sulfur-heterosubstituted 1,3-dienes 77a-d, 79a-d, 87a-d, 88a-d and 89a-d were readily prepared in good to excellent yields by a stereoselective transfer reaction from zirconium. The 1-azadienyl complexes also served as useful starting materials in the preparation of selenium-and phosphorus-substituted 1-azadienes. The selenium-substituted 1,3-dienes 88a-d underwent a facile isomerization reaction when exposed to fluorescent light, and when thermolysed in the dark at 80°C in unsealed reactors. Mechanistic studies of this isomerization process suggested that an intermolecular pathway involving free radical intermediates was operable. A comparable photochemical isomerization reaction of the sulfur-substituted 1,3-dienes was also observed. When the cycloaddition reactions of 88a-b and 88d with maleic anhydride were performed in the absence of light at reson able temperatures, good yields of the expected endo-cycloadducts were obtained. However, when the same reactions were repeated in room light or at temperatures in excess of those required for formation of the endo-cycloadducts an, interesting, apparent [l,3]-shift of the phenylselenenyl moiety resulted. The results of a crossover experiment indicated that this rearrangment was intermolecular in nature. The preparation of the trialkylstannyl and phenylselenenyl 2-substituted 1,3-dienes (128 and 129) was achieved via a transmetalation reaction of the Grignard reagent 24. The Diels-Alder reactivity of 1,3-dienes 128 and 129, with a series of electron-deficient dienophiles, was successfully investigated. [Formula Omitted] / Science, Faculty of / Chemistry, Department of / Graduate

Faculty of Science School of Chemistry 9309501t Stanley.manzini@up.ac.za / The solventless reaction between Mn(CO)4(PPh3)Br and PPh3 as neat reagents using FTIRS was conducted and the activation enthalpy change of formation was found to be 143 ± 19 kJmol-1 while the activation entropy change of formation was 104 ± 7 Jmol-1K-1. The same reaction was also carried out in chloroform and the activation enthalpy change of formation was found to be 146 ± 8 kJmol-1 while the activation entropy change of formation was 114 ± 6 Jmol-1K-1. When the reaction was conducted in TCE solution, the activation enthalpy and entropy changes of formation were 137 ± 6 kJmol-1 and 97 ± 5 Jmol-1K-1 respectively. The solventless reaction of Mn(CO)4(PPh3)Br with PPh3 in KBr matrix using DRIFTS was also conducted and the activation enthalpy change of formation was found to be 169 ± 28 kJ.mol-1 while the activation entropy change of formation was 204 ± 57 J.mol-1.K-1. The sample preparation method, the type of support and the particle size of the support material influenced the reaction rate. The soventless reaction Mn(CO)4LBr + L → Mn(CO)3L2Br + CO [L= P(p-C6H4-R)3, R = Ph, MeO, Cl, F] in KBr using DRIFTS was also studied. It was found that the electronic effects of the ligand already attached on the metal complex influenced the rate of the reaction. An optical microscopy study of the reaction Mn(CO)4LBr + L' → Mn(CO)3LL'Br + CO [L= P(p-C6H4-R)3, R = H, Ph, MeO] was undertaken in an attempt to reconcile the wellbehaved reaction kinetics of the solventless reactions with solventless reactions by observing the microscopic behaviour of the reagents. The reactions were observed to go through a melt phase at temperatures much lower than the lowest melting point of the reagents, provided the reagents were in contact with each other. Isolated reagents neither reacted nor melted. The molten reagent thus served as a medium that allowed the diffusion of the reagents and products to ensure well-behaved kinetics. Investigation using 31P NMR demonstrated that the dissociation of the attached phosphine ligands also iii iv took place. The evidence obtained using the various techniques enabled the elucidation of the reaction mechanism. The solventless reaction, (η5-C5H5)2ZrCl2 + Na+RCOO-, R = C6H5, p-C6H4-NO2, p-C6H4- NH2 → (η5-C5H5)2ZrCl(RCOO) + NaCl did not occur but the reaction was found to take place in the NMR solvent. Single crystal XRD study of (η5-C5H5)2ZrCl(RCOO) R = C6H5, p-C6H4-NO2 revealed that the carboxylato ligand was coordinated in a bidentate fashion. The reaction of chlorobis(η5-cyclopentadienyl)hexylzirconium(IV) with internal hexene isomers failed to yield terminal olefins even under harsh experimental conditions. Isomerisation reactions using substituted zirconium metallocenes also failed to produce the terminal olefin. The reaction of Cp2ZrCl2 / n-BuLi with internal hexenes yielded a stoichiometric amount of 1-hexene. The reaction was found to be catalytic in Cp2ZrCl2 but limited by the amount of n-BuLi.

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Doctor of Philosophy / Department of Chemistry / Eric A. Maatta / The thesis focuses on the design and synthesis of novel organoimido delivery reagents capable of forming bimetallic polyoxometalate (POM) hybrids, and their use in the assembly of bimetallic hexamolybdate derivatives. These delivery reagents have been designed thoughtfully and separate organic moieties have been selected for coordinating to both the POM cluster and the second metal atom. A series of three ligands [4-aminopiperidine, 4-(4-aminophenyl) piperazine, and 4-(4-aminophenyl) piperidine] were selected and used to synthesize the dithiocarbamate metal-coordinating ligands, which in turn were used for preparing the corresponding metal (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag) complexes. All the complexes were characterized by infrared spectroscopy (IR). Reported routes were followed for the covalent grafting of these metal complexes onto hexamolybdate. But, the poor solubility of these metal complexes was found to be a major stumbling block in our endeavors to synthesize the dithiocarbamate based polyoxometalate hybrids. The observed poor solubility of metal dithiocarbamate complexes was overcome by synthesizing [potassium(I) tris(3,5-diphenylpyrazole)borate] and [potassium(I) tris(3,5-dimethylpyrazole)borate] via thermal dehydrogenative condensation between tetrahydroborate and the respective pyrazole molecule. A series of corresponding transition metal (M = Co, Ni, Cu, Mn) complexes of tris(3,5-diphenylpyrazole)borate and tris(3,5-dimethylpyrazole)borate were synthesized, and characterized by IR and UV-visible spectroscopy, and single crystal X-ray diffraction. The single crystal structure of [manganese(II) (tris(3,5-dimethylpyrazole)borate)2] turned out to an outlier as it displayed the formation of a bis-complex, thus having no substitutable anion for further reaction with dithiocarbamates. Thereafter, a series of metal dithiocarbamate complexes of these [hydrotris(pyrazolyl)borates] (M = Co, Ni, Cu ) were prepared using [sodium 4-aminopiperidyldithiocarbamate] and were characterized by IR and UV-visible spectroscopy. A remarkable improvement in the solubility of these metal dithiocarbamates in organic solvents was observed. Furthermore, attempts to covalently graft these complexes onto hexamolybdate cluster were undertaken, and found to be unsuccessful possibly due to the strong oxidizing nature of PPh[subscript]3Br[subscript]2 and hexamolybdate. Although, we were able to successfully tailor the solubility of the dithiocarbamate complexes to suit our needs, our efforts to achieve the primary goal of synthesizing dithiocarbamate based polyoxometalate hybrids have so far been unsuccessful. A series of three pyridyl based ligands i.e., 3,5-di(pyridin-2-yl)-4H-1,2,4-triazol-4-amine, 4-(pyridin-4-ylethynyl)aniline and 4-(pyridin-3-ylethynyl)aniline were synthesized and characterized. Covalent attachment of these ligands to hexamolybdate were attempted following various well-known routes. Although, no evidence of covalent attachment of 3,5-di(pyridin-2-yl)-4H-1,2,4-triazol-4-amine to hexamolybdate was observed, the covalent grafting of 4-(pyridin-4-ylethynyl)aniline and 4-(pyridin-3-ylethynyl)aniline to hexamolybdate cluster was successfully achieved. Characterization of these novel organic-inorganic hybrids was done using IR and NMR spectroscopy as analytical tools. Attempts have been undertaken to obtain single crystals of these hybrids. Also, a novel route involving halogen bonding as a purification and separation technique for pyridyl functionalized hexamolybdate hybrids is also being explored. The novel acetylacetonate moiety has been explored as an imidodelivery reagent for synthesizing hexamolybdate covalent hybrids, wherein [3-(4-((4-aminophenyl)ethynyl)phenyl)-4-hydroxypent-3-en-2-one] ligand has been successfully synthesized and characterized. Traditional methods along with unconventional methods such as heating at elevated temperatures and microwave reaction conditions, have so far proved to be unsuccessful in the synthesis of the hybrids. A series of the corresponding metal complexes have been synthesized and characterized, where the ligand and its corresponding copper(II) complex have been characterized by single crystal XRD. In the crystal structure of the copper complex, the metal ion sits in a slightly distorted square-planar pocket, where no coordination to the -NH[subscript]2 group is observed, which highlights the potential of using it as an imidodelivery reagent.