Chemistry

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Browsing Chemistry by Author "Dube, Zanele Felicia"

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    Synthesis and evaluation of Pd(II) and Ni(II) complexes as catalyst for ethylene polymerization
    (University of Zululand, 2017) Dube, Zanele Felicia; Segapelo, T.V.
    This study entailed the synthesis and evaluation of asymmetric palladium(II) and nickel(II) pyrazolyl hydrazide complexes, C1-C6, as catalyst for ethylene transformation reactions. The complexes were prepared from their respective pyrazolyl hydrazide ligands L5a, L5b and L5c, which were also prepared in this study. The synthesis of all ligands was achieved in five (5) steps from 3-bromomethyl benzoate, L2. Compound L2 was prepared from bromination of methyl 3-methyl benzoate L1, using NBS. Benzene methylene pyrazolyl acids (L3a-L3c) were prepared from the reaction of L2 with different pyrazolyl moieties, namely 3,5-dimethyl pyrazole (Me)2Pz = L3a, 3,5-diphenyl pyrazole (Ph)2Pz = L3b and 3,5-ditertiarybutyl pyrazole (tBu)2Pz = L3c, under basic reaction conditions and were obtained in good yields of between 75-80%. Interestingly, the basic conditions used to anchor the pyrazole moieties readily hydrolyses the ester groups back to their corresponding acids. This meant the esterification reaction to be repeated to turn the acids back to esters for hydrozonolysis to be possible. Thus, preparation of the pyrazolyl hydrazide ligands L5a, L5b and L5c was successfully carried out from the corresponding pyrazolyl esters L4a, L4b and L4c, and the ligands were obtained in moderate yields of between 53-63%. All compounds including the final ligands were characterised using common analytical techniques. The pyrazolyl hydrazide ligands L5a-L5c were successfully complexed with PdCl2(NCMe)2 and NiCl2.DME giving square planar complexes C1-C3 and tetrahedral metal complexes C4-C5, respectively, with a general formula MLCl2. The complexes were obtained in moderate yields of 49-63% and were also characterised using appropriate analytical techniques. The pyrazolyl hydrazide complexes (C1-C6) were successfully evaluated in the ethylene transformation reactions where the catalyst structure, type of solvent used and reaction conditions were found to play a vital role in activity and product distribution. For example, when toluene was used as solvent a mixture of hexene and alkylated toluene products were obtained with hexene and butyltoluenes being the major products. On the other hand running the reactions using chlorobenzene displayed better activities to produce C10-C20 oligomers. The pyrazolyl hydrazide nickel(II) complexes, C4-C6, generally showed better activities when compared to the palladium(II) analogues.
University of Zululand