Department of Chemistry and Polymer Science

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Browsing Department of Chemistry and Polymer Science by browse.metadata.advisor "Brull, R."

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    Novel palladium (II) complexes belonging to a family of potential catalytic precursors
    (Stellenbosch : Stellenbosch University, 2006-12) Blewett, Gavin; Raubenheimer, H. G.; Brull, R.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: This study comprises the preparation and characterization of various novel organometallic complexes of palladium(ll) which contain symmetric and unsymmetric (heteroatom-containing) r..-dicarbonyl-type ligands, T]3-heteroallyl ligands and T]3-coordinated trimethylsilyl-containing ligands. With the ultimate objective of preparing potential catalytic precursors similar to known catalytic precursors which exhibit hemilabile activity, the main goals of this study were the following: - • Investigate the coordination mode of the aforementioned ligand-types to the palladium of the starting compound, trans-[Pd(CeHs)CI{P(CeHshhl (1), by physical measurements. • Carry out single crystal structure determinations where possible. • Investigate the influence of the properties of the ligands on the stability of the prepared complexes. • Investigate the existence of hemilability (if any) in the prepared complex. The deprotonated symmetric and unsymmetric f!,-dicarbonyl-type ligands readily bind to the palladium of the starting compound in a bidentate fashion through the oxygens by displacing a triphenylphosphine group and producing easily removable sodium chloride. These complexes show that a negative charge can be accommodated in a delocalized fashion by the -S=O and - P=O groups of these acac--type ligands in a similar manner to the carbonyl groups of acetylacetonate. However, no evidence of hemilabile activity was found in this series of complexes. In a similar fashion, the deprotonated T]3-heteroallyl ligands, L = [PhzPS£], [PhCOz-], [PhC{NSi(CH3hhl [(Ph)zP{NSi(CH3hh-], were linked to palladium in the same starting complex, in T]3-fashion by triphenylphosphine substitution. No evidence of hemilabilty was evident in this series of complexes, but when L = [PhzPSz-], an exchange of the coordinated triphenylphosphine group with the free triphenylphosphine group was observed in the reaction mixture. Finally, the preparation, isolation and spectroscopic characterization of several T\3-allyl paliadium(lI) complexes with ligands of the type R-TeCH2CH2CQQCH3, (R = isopropyl, t-butyl ,ethyl) were attempted with the compound bis-( T\3-allyl )-di-~ -iodo-dipalladium( II), [T\3 -( CH2CHCH2J2Pd212J, which had also now been crystallographically characterized. Chelate formation by TeAQ coordination seemed possible by halide precipitation with silver tetrafluoroborate. Unfortunately the resulting compounds were too unstable to be isolated in the pure form for characterization.