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dc.contributor.advisorRoodt, Andreas
dc.contributor.advisorBrink, A.
dc.contributor.authorMokolokolo, Petrus Pennie
dc.date.accessioned2018-09-10T11:49:40Z
dc.date.available2018-09-10T11:49:40Z
dc.date.issued2018-02
dc.identifier.urihttp://hdl.handle.net/11660/9271
dc.description.abstractThe principle aim of this study was to investigate the coordination behavior of N,O Schiff-base and oxine-type ligand systems to selected middle and late transition metal carbonyl cores. Firstly, the coordination behavior of Schiff-base bidentate ligands to the fac-[MI(CO)3]+ (M = manganese, technetium or rhenium) was investigated in the context of radiopharmaceutical models. A bidentate ligand can be used in combination with a monodentate ligand utilizing the [2+1] labeling approach, wherein a biologically active component is appended to either the bidentate or the monodentate ligands. Secondly, due to the structural relevance of these ligands systems, the study was extended to investigate their coordination to rhodium(I) as potential supramolecular building blocks for the construction of infinite one dimensional metal chains in the solid state. The oxine ligands systems were incorporated in the investigation to investigate their steric and electronic influence on the assembly of metal-metal chains due to their excellent chelating ability. Moreover, they are known to introduce variations in the metallocycle formed with the rhodium centre (five-membered in oxines vs. six membered for the Schiff-base ligands). With the above in mind, a range of bidentate Schiff-base ligands (5-Me-Sal-CyPentH = 2-(cyclopentyl)methyl-5-methylphenol, (Sal-CyHexH = 2-(cyclohexyliminomethyl-)phenol, 5-Me-Sal-EtPhH = 5-methyl-2-(phenylethyliminimethyl)-phenol and Sal-mTolH = 2-(m-Tolyliminomethyl)phenol, with varying electronic and steric properties were coordinated to the fac-[M(CO)3]+ { M = manganese(I), technetium(I) or rhenium(I)}. Single crystal structures were obtained for complexes fac-[Mn(5-Me-Sal-CyPent)(CO)3]2 (1), fac-[Re(Sal-CyHex)(CO)3]2 (2), fac-[Re(5-Me-Sal-EtPh)(CO)3-(MeOH)] (3), fac-[99Tc(Sal-mTol)(CO)3]2 (4), fac-[99Tc(5-Me-Sal-CyPent)(CO)3]2 (5) and fac-[99Tc(5-Me-Sal-EtPh)(CO)3] (6). The study illustrated that the nuclearity of the rhenium(I) complexes can be manipulated to produce either mono- or dinuclear structures. However, only dinuclear complexes could be isolated with manganese(I) and technetium(I) in spite of employing similar synthesis procedures as for the rhenium(I) complexes. It is postulated that the rhenium mononuclear compound is an intermediate which can be isolated due to the slower reactivity in rhenium complexes, while the increased reactivity in manganese and technetium prevents the isolation of the mononuclear complex. The basic coordination geometry of the mononuclear complex resembles that of the dinuclear one with the metal atom sitting at the centre of an octahedron coordinated by three facially carbonyl ligands, the oxygen and nitrogen atoms of the bidentate chelate. The coordination is completed by a methanol molecule in the mononuclear complex (3), or by the bridging phenolato oxygen atom of the bidentate ligands forming a rigid coplanar system in the dinuclear compound. Rhodium(I) complexes [Rh(5,7-Diido-Ox)(CO)2] (7), [Rh(5,7-DiMe-Ox)(CO)2] (8) and [Rh(5-Me-Sal-iProp)(CO)2] (9) {where 5,7-diido-OxH = 5,7-Diido-8-hydroxyquinoline, 5,7-Dimethyl-OxH = 5,7-Dimethy-8-hydroxyquinoline and (5-Me-Sal-iPropH = 5-Methyl-2-(isopropyliminomethyl)phenol} were synthesized and the electronic and steric effects on the potential assembly of one dimensional metallophilic interactions in the solid state were evaluated. Two classes of rhodium-rhodium interactions were observed from the single X-ray diffraction results. In the one type of interaction, an infinite array of metal-metal interactions occurs in the crystal lattice with a Rh...Rh distance of 3.4602(24) Å for complex (7). In the other type, the rhodium-rhodium interactions are restricted between two neighboring molecules forming pseudo dimeric pairs with the intermolecular Rh...Rh distance of 3.1345(17) Å and 3.6007(10) Å for complexes (8) and (9) respectively. The [Rh(L,L-Bid)(CO)(PPh3)] complexes, where L,L’-Bid is a monocharged bidentate ligand, are fairly well-behaved models in solution for study by 31P NMR, to correlate Rh-P bond distances from solid-state X-ray structural data with observed solution behavior. This study was extended to include solid-state 31P data and a reasonable correlation was obtained. Finally, a kinetic study was conducted to evaluate the reactivity of the rhodium(I) Schiff-base complexes of the form [Rh(Schiff-base)(CO)(PPh3)] towards the oxidative addition of iodomethane thereon. The Schiff-base ligands have varying electronic and steric parameters as informed by the cyclopentyl, isopropyl, cyclohexyl and the methyl substituents attached to the imine nitrogen atom. The effects of these varying factors on the rate of oxidative addition were evaluated in order to further understand the role of the coordinated ligand in this process. Only the formation of the rhodium(III) alkyl species could be observed with no subsequent formation of the rhodium(III) acyl species noted. This is assumed to be due to the slow rate of formation of the acyl species relative to the alkyl(III) product. No significant changes of the activity of the Schiff-base substituents on the rhodium(I) complexes towards the oxidative addition of iodomethane were observed as indicated by the second-order rate constants (k1, M-1.s-1) [Rh(5-Me-Sal-CyPent)(CO)(PPh3)], 0.072(2); [Rh(5-Me-Sal-Iso)(CO)(PPh3)], 0.058(1) and [Rh(Sal-CyHex)(CO)(PPh3)], 0.054(1) in spite of the different substituents incorporated on the ligand backbone. The effect of the tertiary phosphine ligands on the rates of oxidative addition of iodomethane was also evaluated in the complexes [Rh(Schiff-base)(CO)(PPX3)], where PPX3 = PPh3, PPh2Cy, PPhCy2 and PCy3, containing a systematic variation on the substituents of the PPX3. The second-order rate constants (k1, M-1.s-1) for the alkyl formation in the oxidative addition of iodomethane were determined to be [Rh(5-Me-SalCyPent)(CO)(PPh3)], 0.072(2); [Rh(5-Me-SalCyPent)(CO)(PPh2Cy)] 0.146(1); [Rh(5-Me-SalCyPent)(CO)(PPhCy2)], 0.026(5) and [Rh(5-Me-SalCyPent)(CO)(PCy3)], 0.082(1). It was anticipated that the rates would increase with the systematic substitution of the weaker donating phenyl rings on the tertiary phosphine by the more electron-rich cyclohexyl rings. However, the results obtained indicated a somewhat competing effect between the steric and electronic parameters of the phosphine ligands: the observed rates are not in correlation with the electron donating capabilities of the tertiary phosphine ligands. The activation parameters for the oxidative addition of iodomethane to the complex [Rh(5-Me-Sal-CyPent)(CO)2(PPh3)] were determined from a variable temperature study in dichloromethane. An associative type mechanism was assigned for the oxidative addition reaction due to the relatively small Δ𝐻��������≠ = 36(1) kJ mol-1 and a large negative Δ𝑆��������≠ = -145(5) (J K-1 mol) values which are characteristic of an associative type mechanism.en_ZA
dc.description.sponsorshipSASOLen_ZA
dc.description.sponsorshipUniversity of the Free Stateen_ZA
dc.description.sponsorshipNational Research Foundation (NRF)en_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectSolid state chemistryen_ZA
dc.subjectHafnium compounds -- Synthesisen_ZA
dc.subjectZirconium compounds -- Synthesisen_ZA
dc.subjectThesis (Ph.D. (Chemistry))--University of the Free State, 2009en_ZA
dc.titleSolid state and mechanistic study of schiff-base complexes of middle transition and platinum group elementsen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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