Abstract
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