Michael Bertagna
Major/Minor: Biochemistry and Molecular Biology Major/Computer Science Minor
Title: Why Do Counterions Play a Non-innocent Role in Calcium Salt Catalysis?
Abstract: Calcium ions, bound to weakly coordinating anions (i.e., bistriflimide or triflate ions), have gained significant utility within the last two decades as catalysts for facilitating challenging chemical reactions. This is particularly exciting because calcium, unlike the transition metals typically used as catalysts, is exquisitely cheap, abundant, and non-toxic. Despite this obvious advantage, calcium catalysis understanding is in its infancy - we still know very little molecular detail as to the mode in which calcium ions activate substrates in chemical reactions and how the calcium salt facilitates chemical transformations. This lack of mechanistic detail inhibits our ability to design more optimal calcium catalysts that rival the efficiency of transition-metal-catalyzed reactions. Our lab has been investigating calcium ion activation mechanisms in a Sulfur(VI)-Fluorine Exchange (SuFEx) reaction mediated by calcium bistriflimide salts, converting sulfur(VI) fluorides toward nitrogen-containing sulfur(VI) compounds of medicinal relevance. Interestingly, a closer look at the experimental data shows that switching the anion from bistriflimide to triflate results in dramatic loss in reaction yields, indicating that the counterion plays a crucial role in facilitating the chemical process, beyond just being weakly coordinating. In my project, I will use computational chemistry techniques to study the SuFEx mechanism mediated by calcium triflate and compare the geometries, energies, and electronic properties at the resting and activated transition states of the calcium triflate-mediated process to that of calcium bistriflimide to uncover the origins of the counterion-induced reactivity differences between calcium bistriflimide and calcium triflate. In this poster, I will present on my literature review, specific aims, research methodology, preliminary data, and a hypothesis for the role the counterion plays in affecting calcium ion reactivity.
