Ph.D. / In order for any new useful complexes to be developed, whether of catalytic, biological or of other importance, it is very important that sufficient knowledge exists regarding the fundamental principles applying to the chemistry involved. In all chemical processes involving metal complexes, the coordinated ligands govern the reactions to a great extent. It is thus very important that the properties (solubility, reactivity, steric bulk, etc.) of various ligands of these complexes is clearly understood in order to enable intelligent adjustments to be made, inducing the effects of choice. In most catalytic cycles, basic chemical reactions like substitution, addition, oxidative addition and reductive elimination are of importance. Some of the methods used to quantify ligand properties include single crystal X-ray studies as well as investigating various reactions on model square planar complexes. Several problems are normally associated with this type of investigation and are summarized below along with the aims of this study to improve upon this. (i) Very often the Vaska type compounds crystallise on an inversion centre as is shown in a generalized structure in Figure 1.1. This creates several problems ranging from less accurate bond distances/angles to problematic refinement of single crystal data. As the disorder is ruled by symmetry, the occupancies of the disordered atoms are 50%. The example shown in Figure 1.1 is also a fortunate case where the disordered atoms do not have the same positions, making refinement of the data easier, but there are examples27 such as [Pt(Me)Cl(PCy3)2] where the disordered moieties (Me- and Cl-) occupy virtually the same positions. In examples such as these restraints have to be applied, i.e. fixing bond distances to average distances from literature. The important parameter of the ligand trans effect is then meaningless and cannot be reliably compared to data from solution studies. / Prof. A. Roodt
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:12255 |
| Date | 14 October 2008 |
| Creators | Muller, Alfred Johannes |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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