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Thesis (MSc. (Chemistry)) -- University of Limpopo, 2015 / Alkyne-quinoxaline compounds were successfully synthesised form the cross-coupling of 2-benzenesulfonyloxyquinoxaline with terminal alkynes. The current study demonstrates the ability of benzenesulfonyloxy as a good leaving group in Sonogashira coupling reaction, generating a number of alkyne-quinoxaline compounds. The structures of the synthesised compounds were characterised through the comprehensive analysis of spectroscopic data from NMR, HPLC-MS and others selected compounds with IR. Several alkyne-quinoxaline compounds were synthesised in moderate to good yields. During analysis, it was observed that the highest yield was obtained when using 4-(trifluoromethyl)phenylacetylene 4e and the lower yield was obtained when using the 3-ethynylthiophene 4s as a substrate. The alkyne-quinoxaline compounds were investigated for 1,3-dipolar cycloaddition which was done from 2-ethylquinoxaline 6. The 1,3-dipolar cycloaddition reactions were successful and the compounds were obtained in good yields. The in vitro analysis on anti-tubercular screening against H37RvMA strains of M tb reveals that compounds 5e and 5o which contained a trifluoroanisole moiety showed promising activity amongst all the synthesised compounds. The compounds were having MIC90 values 11.8 μM and 12.7 μM respectively, however, they were found to be less active than rifampicin. Compounds 5a, 5b, 5e, 5g, 5h, 5i, 5I, and 5r were evaluated for anti-cancer activity on A549 cells. The results have showed that 5i was able to retard the migration of A549 cells in the Wound-Healing Migration Assay. / National Research Foundation (NRF) Sasol Inzalo Foundation

This thesis describes the synthesis, structure and reactivity of singly bridged dinuclear Group 11 metal complexes, supported by N-heterocyclic carbene (NHC) ligands. These complexes include dinuclear copper(I) complexes that demonstrate three-center, two-electron bonding with short intermetallic distances. In the first part of this study, a hydride-bridged dicopper cation, {[(IDipp)Cu]2(μ-H)}+ BF4–, which adopts a bent arrangement about the hydride was isolated. It undergoes facile methanolysis, readily reacts with carbon dioxide to afford a (κ2-formate)-bridged dicopper species, and coordinates carbon monoxide reversibly to form a carbonyl adduct. The [(LCu)2H]+ cation also inserts phenylacetylene to afford a gem-dicopper vinyl cation, a rare example of the insertion of carbon-carbon multiple bonds into a copper hydride. The second part of this thesis describes the synthesis and structural characterization of the first boryl-bridged dicopper cation {[(SIDipp)Cu]2(μ-B(O2C6H4)}+ BF4–. The solid state structure shows a bent arrangement about the boryl with a short intermetallic distance of 2.4082(2) Å. The boryl-bridged dicopper cation deprotonates phenylacetylene to form a phenylacetylide dicopper complex. It also readily reacts with methanol to form the hydride-bridged dicopper cation. Density functional theory (DFT) calculations were applied to give further insight into the nature of the metal–boron bonds in comparison to the mononuclear analogue. The two electrons contributed by the bridging boryl are shared between the boron and the two copper centers in the [(LCu)2B]+ core. This three-center, two-electron bonding orbital is lower-lying in energy in comparison to the Cu−B σ-bonding molecular orbital in the mononuclear analogue, consistent with a less nucleophilic Cu–B bond. The NHC ligand also stabilizes an isoleptic series of dinuclear μ-fluoro cations of copper(I), silver(I), and gold(I). In these complexes, a single fluoride acts as the sole bridging ligand between the two group 11 metal centers of the form [(LM)2(μ-F)]+. All three cations are highly sensitive to adventitious moisture, readily forming the hydroxide-bridged dinuclear cations. The gold(I) complex is the most reactive. It activates the C-Cl bonds of CD2Cl2 and adds rapidly across an allene C=C bond to form an allylic C–F bond, and a vinyl anion bound asymmetrically to the two gold(I) centers.

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published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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