Lamprecht, G. J.Lamprecht, Delanie2017-06-262017-06-261998-11http://hdl.handle.net/11660/6400English: Four Rh(I)(β-diketonato)(CO)(PPh3) complexes, in which the β-diketone has different electronegativities and steric hindrances, were successfully synthesised and characterised by means of Infrared and NMR spectroscopy. The crystal structure of (1 ,3-Diphenyl-1 ,3-propanedionato-KO, KO) Triphenyl Phosphine Rhodium(I) showed that the asymmetric unit consists of two centrosymmetric pair, but not a crystallographic inversion centre. The partial overlapping of the chelate ring of the one molecule with the phenyl ring of the other molecule can be attributed to π-π interactions between atoms of the two molecules. The oxidative addition kinetics of CH31to Rh(I)(β-diketonato)(CO)(PPh3) complexes was studied in the Visible, Infrared and NMR regions. The proposed oxidative addition mechanism of CH31 to Rh(I)(β-diketonato)( CO)(PPh3) complexes is a nucleophilic attack by the Rhodium atom on the Carbon atom of the methyl iodide, where a linear or a three-centred polar transition state is formed which leads to trans and cis addition respectively. The main purpose of the development of a Rh(I) Carbonyl Phosphine force field was not only to predict the molecular structure of Rh(I) complexes, but also to compute a possible transition states during the oxidative addition of CH31 to Rh(I)(β-diketonato)( CO)(PPh3) complexes. Steric energy calculations indicated that the oxidative addition of CH31to the Rh(I) Carbonyl Phosphine complexes would rather occur via a SN2 mechanism than a concerted three-centred mechanism. The negative entropy of activation and the negative experimental volume of activation obtained during oxidative addition of CH31 to Rh(I)(β-diketonato)( CO)(PPh3) complexes pointed towards an associative mechanism. An increase in solvent polarity leads to an increase in the second order rate constant. These results are indicative of a mechanism where a polar transition state is formed. During the electrochemical oxidation of Rh(I)(β-diketonato)(CO)(PPh3) the only possible co-ordination ligand was the solvent, CH3CN. The addition of solvents with different donosities revealed the co-ordination of the solvents during electrochemical oxidation. The addition of solvents with higher donosities and therefore better coordinating properties made it more difficult to reduce the Rh(III) species formed, back to Rh(I). The two electron irreversible electrochemical oxidation of Rh(I) to Rh(III) was confirmed during bulk electrolysis and Cyclic Voltammetric studies, where the addition of [BzN(Ethtcr to the solution stabilised the formation of Rh(III). The electronic effect of the substituents on the β-diketones showed that the reaction rate increases with the increase of the pKa-values of the freeβ-diketones. The effect of more electronegative substituents on the reactivity of the Rh(I) centre is explained by the fact that electron density is removed from the Rhodium metal, making the complex a stronger Lewis acid and less reactive towards oxidative addition. Steric effects were also perceptible in the present study where the β-diketones, btfa and tfaa, had the same pKa-values. The reaction rate of the bulkier btfa was slower than that of tfaa. Electrochemical oxidation justified the electronic effect, with the exception that steric parameters had no effect during electrochemical oxidation. The oxidation potentials of Rh(btfa)(CO)(PPh3) and Rh(tfaa)(CO)(PPh3), which have the same pKa-values, are the same, within experimental error. The technique of electrochemical oxidation can therefore be used to quantify steric effects during chemical oxidation. The final isomer formed during oxidative addition of CH31 to Rh(I)(β-diketonato)( CO)(PPh3) complexes depends on the nature and nucleophilicity of the ligands. A linear transition state leads to trans addition of CH31, and isomerisation forms a cis Rh(III) Carbonyl Phosphine isomer in the case of Rh(dbm)(CO)(PPh3) and Rh(ba)(CO)(PPh3) as final product. From IR spectroscopy it is clear that the final oxidative addition product of Rh(btfa)(CO)(PPh3) and Rh(tfaa)(CO)(PPh3) is the Rh(III) acyl complex.Afrikaans: Vier Rh(I)(β-diketoon)(CO)(PPh3) komplekse, waar die β-diketone verskillende elektroniese en steriese parameters besit, is suksesvol berei en met behulp van Infrarooi en KMR spektrofotometrie gekarakteriseer. Die kristalstruktuurstudie van (1,3-Difeniel-1,3-propaandionato-KO, KO) trifenielfosfienrodium(I) toon ann dat die asimetriese eenheidsel uit twee onafhanklike molekule bestaan. Die oorvleueling van die chelaatring van die een molekuul met die fenielring van die ander molekuul kan toegeskryf word aan π-π interaksies tussen die atome van die twee molecule. Oksidatiewe addisie kinetika van CH31aan Rh(I) β-diketoon)(CO)(PPh3) komplekse is in die Sigbare, Infrarooi en KMR gebied bestudeer en word voorgestel deur 'n nukleofiele aanval van die Rodiumatoom op die Koolstofatoom van CH31. 'n Liniêre oorgandstoestand of 'n drie-senter oorgangstoestand word voorgestel. Die liniêre oorgangstoestand lei tot frans-addisie van CH31en die drie-senter oorgangstoestand lei tot cis-addisie van CH31 Molekulêre meganika is gebriuk om 'n Rh(I)-karbonielfosfien kragveld te ontwerp waarmee nuwe Rh(I)-karbonielfosfien strukture voorspel kan word, asook om die oorgangstoestand tydens oksidatiewe addisie te bereken. I Die berekening van die steriese energië van beide die liniêre oorgangstoestand en drie-senter oorgangstoestand het aangetoon dat die liniêre oorgangstoestand meer stabiel is en dat oksidatiewe addisie van CH31dus eerder via 'n SN2-meganismesal plaasvind. Negatiewe aktiveringsentropie en aktiveringsvolume waardes wat verkry is tydens oksidatiewe addisie van CH31aan Rh(I)(β-diketoon)(CO)(PPh3) komplekse dui op 'n assosiatiewe meganisme. 'n Verhoging in die polariteit van die oplosmiddels tydens oksidatiewe addisie het gelei tot 'n verhoging in die reaksietempo, wat dui op 'n polêre oorgangstoestand. Slegs die oplosmiddel, CH3CN, is beskikbaar om te koordineer tydens die elektrochemiese oksidasie van Rh(I) na Rh(III). Oplosmiddels wat oor beter doneringsvermoë beskik en dus ook beter koordineer. stabiliseer die gevormde Rh(III) wat die reduksie daarvan terug na Rh(I) bemoeilik. Die twee-elektron onomkeerbare elektrochemiese oksidasie van Rh(I) na Rh(III) is tydens Totale-elektroliese en Sikliese Voltammetrie waargeneem waar [BzN(Et)3]+CI- by die oplossing gevoeg is om die gevormde Rh(III) te stabiliseer. reaksietempo tydens oksidatiewe addisie. Elektron ontrekkende groepe 'n Verhoging in die pKa-waarde van die β-diketoon het gelei tot 'n verhoging in die gekoordineerd aan die Rodium metaal veroorsaak dat die Rodium senter 'n sterker Lewis-suur is en dus minder reaktief is ten opsigte van oksidatiewe addisie. Die reaksietempo wat tydens oksidatiewe addisie van CH31 aan Rh(I)(β- diketoon)(CO)(PPh3) komplekse waargeneem is, is nie net afhanklik van die elektronies parameters nie, maar is ook afhanklik van steriese hindernisse wat deur gekoordineerde ligande veroorsaak word. Rh(btfa)(CO)(PPh3) het dieselfde pKawaarde as Rh(tfaa)(CO)(PPh3), maar die oksidatiewe addisie reaksietempo van die eersgenoemde kompleks was baie stadiger as gevolg van steriese hindernis. Die oksidasie potensiaal van Rh(btfa)(CO)(PPh3) en Rh(tfaa)(CO)(PPh3) wat oor identiese pKa-waardes beskik, was binne 'n eksperimentele fout dieselfde tydens elektrochemiese oksidasie. Alhoewel die elektroniese effek van die gekoordineerde β-diketone dieselfde resultate getoon het tydens chemiese- en elektrochemiese oksidasie, speel die steriese effek van gekoordineerde β-diketone nie 'n rol tydens elektrochemiese oksidasie nie. Die eindproduk van oksidatiewe addisie is afhanklik van die aard en nukleofiliteit van die gekoordineerde ligande. In die geval van Rh(dbm)(CO)(PPh3) en Rh(ba)(CO)(PPh3) is die eindproduk die cis-Rh(III)-karbonielfosfien isomeer, maar in die geval van Rh(btfa)(CO)(PPh3) en Rh(tfaa)(CO)(PPh3) is die eindproduk die Rh(III)-asiel isomeer.enElectrochemical analysisRhodiumReaction kineticsThesis (Ph.D. (Chemistry))--University of the Free State, 1998ThesisUniversity of the Free State