The development of discrete yttrium(III) complexes for the production of biodegradable polyesters

Despite their unique chemical and physical properties, the lanthanides have been relatively unexplored as reagents for selective organic synthesis. This thesis describes the development of a series of yttrium(III) complexes designed for the ring-opening polymerization of cyclic esters, an important group of monomers whose biodegradable polymers have drawn considerable interest in both industry and academia. Six discrete yttrium(III) complexes were prepared using both hydrotris(pyrazolyl)borate and hexadentate macrocyclic ligands; characterization of these complexes with techniques including 1H NMR and X-ray crystallography revealed each to exhibit novel coordination environments for their respective ligand topologies. Five of these complexes were found to be active catalysts for the polymerization of D, L-lactide. Within this series, differences in ligand substituents; and/or the presence of coordinated exogenous molecules such as water and benzyl alcohol were found to influence not only the rates and mechanisms of polymerization but also the molecular weights of isolated lactide polymers. Thus, relationships between the structures and activity of these five catalysts were established, providing novel insights for the future development of related lanthanide polymerization catalysts.