Supramolecular control of regioselectivity in the hydroformylation reaction Substrate preorganization and second coordination sphere catalysis

In this thesis supramolecular strategies were investigated to obtain control over the regioselectivity in the hydroformylation reaction. In the hydroformylation reaction a double bond is reacted with syngas mixture (H₂:CO) in the presence of a transition metal catalyst. Since the aldehyde can add on both sides of the double bond, this reaction has an inherent regioselectivity problem. Ligands can be coordinated to the catalytically active metal center to obtain control over the regioselectivity. This strategy is however not always successful and therefore supramolecular strategies were used in this thesis to obtain control over the regioselectivity for substrates that are difficult to control via traditional strategies in homogeneous catalysis. One strategy involves hydrogen bonding of the substrate to the catalyst to restrict the movement of the substrate during the reaction. Another strategy that is used involves the use of a supramolecular capsule around the metal center. For both strategies, the substrate movement is restricted and as a result the regioselectivity is controlled. Chapter 2 describes a computational investigation for why the hydrogen bonding based catalyst gives the regioisomeric outcome that is observed catalytically. Chapter 3 demonstrates first the regioselective conversion of natural fatty acids in the hydroformylation reaction with a tailor made ligand. Chapter 4 describes the a novel class of ligands for regioselective conversions via hydrogen bonding. Chapter 5 reports how the regioselectivity control of a catalyst varies when structural elements of substrates are varied. Chapter 6 investigates if descriptors of the substrate can be used to predict the regioselectivity of encapsulated and unencapsulated catalysts.