Master of Science
Blacquiere, Johanna M.
The reactivity and coordination of a phosphine-1-azaallyl (P^AzA) ligand was explored using palladium (Pd) and ruthenium (Ru) complexes. Small molecules, H2, O2, and organic acids were added to a Pd(II) dimer to explore small molecule activation with a complex bearing a structurally responsive ligand. Notably, the 1-azaallyl moiety of a Pd(II) dimer was proton-responsive toward H2 and organic acids may be harnessed under catalytic conditions. The possible coordination modes of the P^AzA ligand were further explored by synthesising a Ru-P^AzA complex. The compound was proposed to exist in an equilibrium of three complexes that stabilise the Ru-center, suggesting a coordination site is easily accessible by a substrate. Preliminary experiments with pyridine or phenylacetylene and the Ru-P^AzA complex indicated a coordination site was accessible within seconds. Notably, reactivity studies suggested the Ru-P^AzA complex could be an active catalyst for alkyne cyclisation.
Summary for Lay Audience
Catalysis describes the process of a compound (i.e., a catalyst) speeding up the rate of a chemical reaction. To do this, a catalyst must be highly reactive under the right conditions to facilitate a specific chemical reaction. Ideally, a catalyst can cleanly synthesise a product repeatedly, over long periods of time. This can be difficult to achieve for all catalysts because catalysts can decompose. Sometimes before the desired chemical transformation starts, a fast side reaction(s) can occur that renders the catalyst inactive. When this happens the amount of product achieved could be reduced or none observed. Chemists have thus been exploring methods of limiting catalyst decomposition throughout the years. One notable method has been the addition of an organic functionality to a metal to promote reactivity and/or stabilise the metal throughout the catalytic cycle. The main goal of my study was to expand upon such research; to address the issue of catalyst decomposition through the addition of a novel organic functionality to a metal that has been proposed to reversibly stabilise a metal centre. If the metal center was only partially and reversibly stabilised under catalytic conditions this could prevent undesired side reactions that lead to catalyst decomposition, while still keeping the catalyst reactive. To study this, two metal-organic compounds were explored that contained a novel partially stabilising organic functionality, nicknamed “P^AzA”. Specifically, a sought-after ruthenium-P^AzA compound was made cleanly for the first time. The synthesis of this compound suggested the P^AzA was able to partially and reversibly stabilise ruthenium readily at room temperature. Additionally, the preliminary chemical reactivity of the ruthenium- and palladium-P^AzA compounds were explored to understand the implications of the P^AzA group on a chemical transformation. These reactivity studies suggested that the P^AzA group was able to promote desirable reactivity with some organic substrates (i.e., alkynes) and that acidic environments may be exploited for catalysis.
Kindervater, Meagan, "Coordination and Reactivity of a Structurally Responsive Phosphine-1-Azallyl Ligand" (2020). Electronic Thesis and Dissertation Repository. 7504.