Complexes of Bismuth and Indium Supported by Pincer Ligands

Abstract

This thesis discusses the use and effects of pincer ligands on complexes of the heavy p-block elements bismuth and indium. Pincer ligands, originally developed for and widely used in the context of transition metals, have recently found applications in main group chemistry. Pincer ligand-supported main group compounds are often used to perturb the geometry of these metal centres away from the valence shell electron pair repulsion (VSEPR) theory-predicted minimum energy geometry. These VSEPR non-compliant main group compounds are of interest due to the unique properties and reactivity these geometries unlock at the inorganic element centres. This Thesis first explores the electronic and geometric tuning of a series of planar bismuth compounds. The introduction of electron-withdrawing groups onto the ligand backbone resulted in increased Lewis acidity at the bismuth centre, a property which could be tuned by selecting the ligand substituents. The Lewis acidity for a family of these planar bismuth compounds was assessed using a variety of experimental and computational methods, and these complexes were exploited for the ring-opening polymerization (ROP) of lactones. A detailed computational investigation for a family of 64 pincer-supported pnictogen compounds was also undertaken, looking at the four heavier pnictogens with a set of 16 different ligands. These computational results were used to propose a model to explain the geometries of pincer ligand supported pnictogen compounds, between the two commonly observed geometries of T-shaped and pyramidal. Phosphorus and bismuth complexes of a unique, all-inorganic pincer ligand were also accessed, finding different geometric outcomes depending on the oxidation state of phosphorus atoms in the ligand backbone. Pincer ligand-supported indium complexes were investigated, first looking at complexes in the + 3 oxidation state. A T-shaped tricoordinate structure was targeted, with preliminary efforts instead yielding four- and five-coordinate indium species supported by pincer ligands. Indium(I) compounds supported by pincer ligands were also targeted, and while an In(I) complex has yet to be isolated, preliminary results point towards the transient formation of the targeted species. This transient In(I) complex has been found to be capable of exciting chemical transformations, including oxidative addition and C-C bond formation.