M.Sc. / The main objective of the research described in this dissertation was to prepare several logical series of ligands, being variously substituted at different positions of the aryl ring attached to the P atom. These ligands were evaluated by several techniques including 31P NMR shift measurements, 31P-77Se NMR coupling constant measurements, CO stretching frequency measurements in rhodium(I) Vaska-type complexes of the ligands, application of the ligands in the Rh-catalysed hydroformylation reaction, X-ray studies on single crystals of some of the ligands and computational studies all with the view to establish if phosphorus atoms in arylphosphines could be used as a handle to probe steric and electronic effects of aromatic systems. A series of triarylphosphine ligands containing either ester, fluoro, nitrile, tolyl or a combination of functional groups was prepared by reacting Grignard- or organolithium reagents with P-Cl reagents. The results of this aspect of the work showed that, under the right reaction conditions, these organometal reagents can tolerate certain functional groups. On evaluation of these ligands with the different techniques described above it was found that: 31P NMR shift measurements cannot be used in correlations with the data from the other methods of evaluation used in this study, 31P-77Se coupling constant measurements and CO stretching frequency measurements in rhodium(I) Vaska-type complexes of the ligands can be correlated to a relatively good extent with Rhcatalysed hydroformylation reaction results (provided that ortho-substituted phosphine data are disregarded), 31P-77Se NMR coupling constant measurements and CO stretching frequency measurements in rhodium(I) Vaska-type complexes of the ligands correlated well with computational studies, and finally, computational studies at the level of theory used in this dissertation also correlate quite well with the Rh-catalysed hydroformylation reaction results. In all it was found from this study that the phosphorus atom in arylphosphines can be used as a handle to probe the electronic and steric effects of aromatic systems, and that the most versatile method of ligand evaluation were the 31P-77Se coupling constant measurements and CO stretching frequency measurements in rhodium(I) Vaska-type complexes.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:7065 |
| Date | 16 May 2011 |
| Creators | Miller, Stuart Frank |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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