The objective of the research described in this dissertation was the search for optimum ligand-metal complex combination that would facilitate the contrathermodynamic isomerisation of internal olefins. To this end a variety of ligands where synthesised and subsequently tested, firstly for their ability to isomerise alpha olefins and secondly their ability to isomerise internal olefins. Due to the lack of information obtainable from literature about catalytic isomerisation of olefins, the general reaction parameters had to be investigated. Various factors that could play a role in the isomerisation of olefins where investigated and these included the effect that solvents have on the isomerisation as well as the possibility of metalhydride formation. The possible formation of metal-hydrides was tested by adding a variety of acids and also the addition of hydrogen gas to the solution. All of these factors played an important role in the subsequent isomerisation of alkenes and valuable data could be obtained from these experiments. Solvents were found to have an effect on the isomerisation, but a trend could not be established. The effect of added acid was more pronounced and a correlation between acid strength and isomerisation could be established. It was also found that hydrogen gas added to the reaction mixture generally increased the reactivity of the metal catalysts and some experiments were done to optimise the use of hydrogen in these reactions. The use of commercially available ligands for the isomerisation reaction was also investigated and gave a broad indication of possible active ligands. After these initial reactions and information gathered from literature, it was decided to synthesise a set of di-imine ligands and also a set of bis-phisphite ligands. Due to tautomerism of the di-imines to the corresponding enamines, a set of enamine/imine ligands was synthesised and tested with two rhodium and two palladium catalysts. The synthesis of bis-phosphite ligands was initially problematic, but ideal conditions were found and a set of bis-phosphite ligands was synthesised and tested. Results obtained from the testing of both the enamine/imine lignds as well as the bisiii phosphite ligands were of value and a great many trends could be observed. Many of these observations had correlations to either the electronic nature of the various ligands as well as that of the metal centre. The testing of a set of palladium(II) metallocycles also gave an insight into the electronic properties necessary for the successful isomerisation of olefins. These electronic properties are always a combination of ligand and metal centre effects and thus a fine balance must be struck between these two factors. As a final conclusion to the work that was performed, internal olefins were subjected to tandem isomerisation-hydroformylation reactions using some of the more active metal-ligand systems. Internal olefins were isomerised and hydroformylated in the same reaction vessel to afford branched and linear aldehydes. In these reactions, it was proved that isomerisation as a primary reaction could be coupled to a secondary reaction and be of use in industry and further research in this field might prove to be of some value. / Prof. D.B.G. Williams
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:7222 |
| Date | 14 May 2008 |
| Creators | Kriel, Frederik Hermanus |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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