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dc.contributor.advisorRoodt, Andreas
dc.contributor.advisorVisser, Hendrik G.
dc.contributor.authorCloete, Nicoline
dc.date.accessioned2018-09-14T11:55:50Z
dc.date.available2018-09-14T11:55:50Z
dc.date.issued2010-01
dc.identifier.urihttp://hdl.handle.net/11660/9302
dc.description.abstractEnglish: Transition metal-catalyzed ethylene oligomerization typically produces a broad range of α-olefins. The selective tetramerisation of ethylene to 1-octene is possible with the use of diphosphinoamine ligands together with chromium(lll) and an aluminoxane activator as catalyst system. The aim of this study was therefore to synthesize and characterise a range of diphosphinoamine (PNP) ligands with varying catalytic activity and selectivity (see Figure 1). The stereo-electronic properties of these ligands were evaluated by varying the alkyl group in a systematic way. The single crystal X-ray crystallograph ic study of the above-mentioned PNP ligands revealed a decreasing trend of the P-N-P bond angle to decrease as the steric bulk of the alkyl moiety increases. Figure in PDF full text. An important part of this investigation was concerned with the synthesis and evaluation of the solid state characteristics of the PNP ligands bonded to Cr(lll). This was extended by complexing other metal cations (eg. Pt(ll) and Pd(ll)) with the various PNP ligands in order to provide further information on the coordination mode of these ligands. The study was also supplemented with theoretical chemistry. The comparison between the optimised structure and the crystal data revealed small differences, resulting in the possibility that predictions can be made in terms of ligand design. The calculated structure indicated that the phenyl ring arrangement is affected by the steric bulk of the nitrogen-coordinated alkyl moiety which could ultimately affect the catalytic selectivity. A steric parameter was defined (Effective Tolman-based N-substituent steric effect (θN·sub)) in which the steric bulk of the nitrogen-coordinated alkyl substituent was quantified. A comparison between θN·sub for various diphosphinoamine ligands (free and metal-coordinated) and the catalytic selectivity (for 1-C6 and 1-C8) revealed a relatively good correlation with the catalytic selectivity increasing as θN·sub for the varying ligands increased. It was also possible to compare the θN·sub* (from theoretically calculated structures) with the catalytic selectivity and a similar trend was observed for the optimized structures than the solid state structures (θN·sub). The kinetics of the substitution of two chlorido ligands of the [PtCl2(PNP-i-Pent)] complex with Br- was investigated. Two consecutive reversible reactions were observed and analysed separately. Three platinum(II) species [(PtCl2(PNP-i-Pent)], [(PtBrCl(PNP-i-Pent)] and [(PtBr2(PNP-i-Pent)], are present in equilibrium after the completion of the two reactions and was characterized with 31P NMR. An associative mechanism was identified for both reactions, with large negative entropy and low positive enthalpy values.en_ZA
dc.description.abstractAfrikaans: Oorgangsmetaal gekataliseerde etileen oligomerisering produseer tipies 'n wye verskeidenheid van α-olefiene. Die selektiewe tetramerisasie van etileen na 1-okteen word gedoen deur difenielfosfino-amien ligande, Cr(lll) en 'n alumienoksaan as aktiveerder as katalissisteem te gebruik. Die doel van hierdie studie was die sintese en karakterisering van 'n reeks difosfino-amien (PNP) ligande wat verskil in terme van katalitiese aktiwiteit en selektiwitieit (sien Figuur 1 ). Die stereo-elektroniese eienskappe van hierdie ligande is evalueer deur die alkielsubstituent sistematies te verander. Die enkelkristal X-straal kristallografiese studie van die ongebonde PNP ligande het aangedui dat die P-N-P hoek afneem soos wat die steriese bonkigheid van die alkielgroep toeneem. Figuur in PDF volteks. 'n Belangrike deel van hierdie ondersoek het die sintese en vaste toestand eienskappe van chroom(lll)-PNP komplekse behels. Dit is verder gevoer deur ook ander metaalkatione (bv. Pt(ll) en (Pd(ll)) met die verskeidenheid PNP ligande te komplekseer om meer inligting omtrent die koordinatiewe eienskappe van hierdie ligande te ondersoek. Hierdie studie is aangevul met berekeningschemie. Die vergelyking tussen die ge-optimiseerde (berekende) strukture en die kristaldata het klein verskille getoon, met die gevolg dat dit in die toekoms moontlik sal wees om voorspellings in terme van ligand ontwerp te bewerkstellig. Die berekende strukture het getoon dat die fenielring rangskikking meestal deur die steriese grootte van die stikstofgebonde alkielgroep geaffekteer word en dat dit 'n groat invloed op die katalitiese selektiwiteit uitoefen. 'n Steriese parameter is gedefinieer (Effektiewe Tolman-gebaseerde N-substituent steriese effek ((θN-Sub) waarmee die steriese hindering van die stikstof-gekoordineerde alkielgroep gekwantifiseer word. 'n Vergelyking tussen die θN-Sub en die verskeie difenielfosfino-amien ligande (vry en gebonde) en die katalisselektiwiteit (vir 1-C6 en 1-C8) het 'n goeie korrelasie tussen stygende selektiwiteit getoon soos wat θN-sub grater word. Dit was ook moontlik om die as θN-sub* (van berekende strukture) met die katalitiese selektiwiteit te vergelyk en 'n ooreenstemmende tendens kon tussen die berekenings chemie en die ware vaste toestand waarnemings getref word. Die kinetika van die substitusiereaksies van die twee chloorligande deur bromied in [PtCl2(PNP-i-Pent)] is ook ondersoek. Twee opeenvolgende, omkeerbare reaksies is waargeneem en kon onafhanklik van mekaar bestudeer word. Drie platinum(ll) spesies [(PtCl2(PNP-i-Pent)], [(PtBrCl(PNP-i-Pent)] en [(PtBr2(PNP-i-Pent)], is in ewewig en is gekakateriseer met behulp van 31P NMR. 'n Assosiatiewe meganisme is vir beide reaksies voorgestel en bevestig deur die hoe negatiewe entropie en lae positiewe entalpiewaardes.en_ZA
dc.description.sponsorshipSasolen_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectLigandsen_ZA
dc.subjectCatalystsen_ZA
dc.subjectMetal complexesen_ZA
dc.subjectEthylene oligomerizationen_ZA
dc.subjectDiphosphinoamine (PNP) ligandsen_ZA
dc.subjectThesis (Ph.D. (Chemistry))--University of the Free State, 2010en_ZA
dc.titleEthylene tetramerization: structure and reactivity investigation of metal based catalyst precursorsen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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