Ligand based encapsulation strategies in homogeneous catalysis

The development of catalysts has enabled highly specialized processes that are of great value to mankind. A relatively new strategy for the development of new homogeneous catalysts involves the use of supramolecular capsules. The encapsulation of homogeneous catalysts in molecular capsules is of interest as activity, selectivity and stability can be controlled by the capsule, which acts as second coordination sphere, reminiscent of how enzymes control chemical reactivity. Homogeneous catalysts however, are not static guest molecules as catalysts change in shape, charge and polarity during the catalytic cycle, representing the challenges involved in capsule controlled catalysis. To address the problems associated with catalyst encapsulation, we developed the ‘ligand-template approach’, which focusses on using the properties of a ligand molecule to encapsulate homogeneous catalysts. We have used the ligand template approach to encapsulate rhodium hydroformylation catalysts in cages suitable for switchable catalysis and in chiral capsule, leading to asymmetric catalysis. In addition to the ligand-template approach we have developed the ‘ligand based encapsulation’ strategy, which is the general approach of using the properties of a ligand molecule to both bind to a transition metal atom and to a supramolecular capsule. In this thesis we use this approach to affect catalysis in rhodium catalyzed hydroformylation and ruthenium catalyzed ring-closing metathesis reactions.