Doctoral Degrees (Chemistry)
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Browsing Doctoral Degrees (Chemistry) by Author "Bala, Muhammad Dabai."
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Item Activation of n-octane and cyclohexane to oxygenates using modified zeolites.(2014) Cele, Mduduzi N.; Friedrich, Holger Bernhard.; Bala, Muhammad Dabai.Three types of zeolites namely ZSM-5, Faujasite Y and MOF-5 were synthesized. The synthesis of Na-Fe-silicalite-1(34), H-Fe-silicalite-1(34), Na-Fe-silicalite-1(41), Na-Fe-silicalite-1(68), Na-Fe-silicalite-1(80), Fe-silicalite-1(128), Na-Fe-ZSM-5(66) and Na-Fe-ZSM-5(114) was conducted using a solid gel method. Further to this, Na-Fe-silicalite-1(41), Na-Fe-silicalite-1(80), Fe-silicalite-1(128), Na-Fe-ZSM-5(66) and Na-Fe-ZSM-5(114) were modified by silanisation using tetraethoxysilane (TEOS) as the silanisation agent to produce Na-Fe-silicalite-1(41:Sil), Na-Fe-silicalite-1(80:Sil), Na-Fe-silicalite-1(128:Sil), Na-Fe-ZSM-5(66:Sil), Na-Fe-ZSM-5(114:Sil). The numbers in brackets represent Si/Fe molar ratio while Sil represent silanisation. Powder XRD results showed that only the ZSM-5 phase was obtained. The second type was synthesized by encapsulation of Fe-TPP (tetraphenylporphyrin) inside faujasite Y to produce Fe-TPP-NaY. Powder XRD results confirmed the faujasite structure after encapsulation. Finally, Fe-MOF-5(1), Fe-Zn-MOF-5(0.5) and Fe-Zn-MOF-5(0.2) were synthesized using conventional methods with the numbers in brackets representing the Fe wt%. Also, XRD results showed that the MOF-5 phase was obtained with a sharp peak at 2θ below 10° which is characteristic of a highly crystalline material. All synthesized catalysts were tested in the oxidation of n-octane to oxygenates with H2O2 as the oxidant in MeCN. Furthermore, Fe-TPP-NaY was also used to activate 1-octene, 4-octene and cyclohexane while Fe-MOF-5 was used to activate cyclohexane. Na-Fe-silicalite-1(34), H-Fe-silicalite-1(34) and Na-Fe-silicalite-1(68) produced selectivities of 24, 2 and 27% respectively to terminal products at 80 °C in 13 mL MeCN. Furthermore, Na-Fe-silicalite-1(41), Na-Fe-silicalite-1(80), Fe-silicalite-1(128), Na-Fe-ZSM-5(66) and Na-Fe-ZSM-5(114) achieved selectivities to terminal products of 20.2, 28.1, 17.6, 24.5 and 21.3 respectively while Na-Fe-silicalite-1(41:Sil), Na-Fe-silicalite-1(80:Sil), Na-Fe-silicalite-1(128:Sil), Na-Fe-ZSM-5(66:Sil) and Na-Fe-ZSM-5(114:Sil) showed selectivities to terminal products of 20.7, 14.3, 12.3, 25.7 and 27.3 % respectively at 80 °C in 80 mL MeCN. Fe-TPP-NaY showed 13% selectivity to terminal products in oxidation of n-octane at 80 C in 13 mL MeCN. In the oxidation of n-octane using Fe-MOF-5 catalysts, selectivity to terminal products was found to increase with a decrease in the wt% of Fe. Hence, selectivities of 9.5, 12.9 and 20.7% were recorded for Fe-MOF-5(1), Fe-Zn-MOF-5(0.5) and Fe-Zn-MOF-5(0.2) respectively.Item Exploration of triazolylidene metal complexes of Fe, Ni and Cu : synthesis, characterization and applications in oxidation catalysis.(2018) Mncube, Siyabonga Gift.; Bala, Muhammad Dabai.Abstract available in PDF file.Item N- and S-donor pincer complexes of Ni and Cu: synthesis and application as catalysts in alkane oxidation.(2017) Soobramoney, Lynette.; Bala, Muhammad Dabai.; Friedrich, Holger Bernhard.Abstract available in PDF file.Item N-heterocyclic carbene-iron(II) complexes : chemistry and application as transfer hydrogenation catalysts.(2011) Ikhile, Monisola Itohan.; Bala, Muhammad Dabai.; Nyamori, Vincent Onserio.In the last decade N-heterocyclic carbene (NHC) ligands have become important in organometallic chemistry and homogeneous catalysis, rivalling the well established phosphines. Most of the current attention to date has focused on the NHC complexes of the platinum group metals (rhodium, palladium and nickel) plus ruthenium based system, but the chemistry of NHC systems of iron which is relatively inexpensive and environmentally friendlier is considerably less developed. Thus, this project involves the design, synthesis, characterization and application in catalytic transfer hydrogenation of NHC ligands and their iron(II) complexes. The motivation for the choice of NHC as a ligand stems from the ability to systematically tune the ligand both electronically and sterically in addition to the stability and robustness of the ligand to stabilize metal centres in various environments. In this research imidazolium based NHCs are generated. Thus, three different series of imidazolium salts were synthesized and their iron(II) complexes was obtained. All the compounds were characterized by spectroscopic and crystallographic methods. These are: (a) 1,3-dialkylimidazolium salts (b) 1,3-diarylimidazolium salts and (c) ferrocenylimidazolium salts bearing methyl and phenyl spacers between the ferrocenyl and the imidazolium moieties. A total of 20 novel compounds were synthesized and are reported in this thesis. Furthermore, the application of the new compounds as transfer hydrogenation catalysts was investigated using 17 saturated and unsaturated ketones as substrates, in the presence of KOH as the base and 2-propanol as the hydrogen source. The dialkylated NHC iron(II) complexes showed excellent yields, and TON values of up to 200 were achieved under the optimized reaction conditions. Without complexation with iron, the 1,3-diarylimidazolium and ferrocenylimidazolium series of salts were also found to be active catalysts for the transfer hydrogenation reaction of ketones in alcoholic media. In the case of ferrocenylimidazolium salts a TON value up to 1880 was achieved. Notably, two of the unsaturated ketones were successfully converted at a high yield with a high selectivity to the corresponding saturated ketones only. In addition, the stability of NHC ligands to moisture was investigated, since an understanding of the stability of various deprotonated NHC-based imidazolium cations to attack by moisture resulting in hydrolysis products is very important to understanding the coordination chemistry of the ligands on to metal centres. Four novel ionic diamino aldehyde compounds were obtained by moisture attack on saturated NHC ligands. The route to the formation of the hydrolysed compounds is formulated to occur via an imidazolinium ring opening process. On the other hand the unsaturated counterparts were more stable towards hydrolysis yielding adducts with the iron(II) precursors. Finally, the electrochemical properties of the ferrocenylimidazolium salts were investigated using cyclic voltametry. By comparing the relative shifts in the formal electrode potentials of the ferrocene/ferrocenium coupled with the ferrocenylimidazolium salts, it was easy to evaluate the influence of the substituents on the carbene containing imidazolium moiety on the electrochemical properties of the iron centres. The formal electrode potential of the ferrocenylimidazolium salts shifted to higher positive potentials as compared to ferrocene, indicating a high electron withdrawing effect of the imidazolium salts. This makes the metal centres more vulnerable to attack by nucleophiles. The electrochemical studies have enabled a structure-activity correlation to be drawn for the various ferrocenylimidazolium salts.Item Synthesis and characterisation of chelating, hemilabile N-Heterocyclic carbene ligands : applications of their cobalt (II) and nickel (II) complexes as catalysts for aryl amination.Ibrahim, Halliru.; Bala, Muhammad Dabai.The chemistry and applications of N-heterocyclic carbenes (NHCs) as ligands for the preparation of transition metal complexes has remained at the forefront of research in organometallic chemistry and homogeneous catalysis worldwide. This is evidenced by the increasing number of research articles on the subject area. Hence, this thesis report on three different ligand frameworks consisting of a symmetric CNC pincer architecture and two non-symmetric N-substituted imidazoles bearing a picolyl and a ferrocenylphenyl imidazole functionalities. These were then used to synthesise new ligand precursors (imidazolium salts) which were later on complexed to Ni and Co via transmetalation of corresponding NHC-Ag complexes. The synthesis of the pincer imidazolium salts via a solvent free method led to the development of a new technique based on the use of a short plug of silica to purify such salts and isolate them in excellent yields. This method has been published and is now adopted in our laboratory and extended to the purification of a wider variety of salts including those based on the related triazolium moiety. All the compounds (salts and metal complexes) have been fully characterised by NMR (1H, 13C, 31P), IR, HRMS or MS-ES+, EA and in some cases single crystal X-ray diffraction analyses. Sharp melting points were also recorded for all air stable, none hygroscopic compounds. The characterisation data have established the chemical composition and purity of all the compounds reported in this thesis. All the complexes are active as catalysts for the activation of C-N coupling of aryl amines and aryl halides. The catalyst systems showed excellent selectivity to N-mono arylation as no trace of N,N-diarylated products were observed. The high selectivity and excellent yields to desired products achieved under mild reaction conditions and low catalyst loading of 1 mol% of Ni or Co has made the current catalyst systems competitive in comparison to classical Cu mediated or CuI catalysed Ullman coupling and Pd catalysed systems. A highly active in situ generated NiCl2/imidazolium salt catalyst was also developed, hence opening up a simple, robust and functional group tolerant system for C-N coupling reactions that may easily be generated from commercially available imidazolium salts in combination with over the counter metal salts such as NiCl2.