Note: ROSEI is cohosting this seminar with the Department of Chemistry.

Title: Combining Photophysics and Inorganic Synthesis to Target Small Molecule Activation and Production: From Methane to Ammonia

Abstract: The transformation of small molecules into more valuable and complex materials represents a persistent challenge of chemistry. Often the activation of these small molecules, such as methane and dinitrogen, is made difficult due to both high entropic and enthalpic barriers. In recent years, chemists have turned to visible light photons to provide the energy to overcome these barriers. Towards the activation of methane and other simple hydrocarbons, I utilized the hexachlorotitanate (TiCl62-) dianion as both the photoactive species and the source of highly reactive chlorine radical. This system resulted in enhanced reactivity in the scope of radical acceptor compared to the similar hexachlorocerate (CeCl62-). Using a combination of electrochemistry, single crystal x-ray diffraction, and density functional theory, I identified the chemical differences between the titanium and cerium systems that led to their distinct reactivity. Expanding on hte activation of small molecules, I focused on the light-mediated reduction of metal nitrides into ammonia. While published work on manganese nitrides had focused on the identity of the photocatalyst, the reaction was found to work in the absence of precious metal photocatalyst. Optimization of the ligand supporting the manganese nitrides brought ammonia yields to 80%, higher than when a photocatalyst was included in the reaction mixture. Using transient absorption spectroscopy, the photoactive species was then determined. Preliminary investigation of the synthesis, reactivity, and photophysics of group 6 metal nitrides will also be discussed. Together, these results highlight the utility of spectroscopic methods in tandem with synthetic inorganic chemistry to develop and understand methods of small molecule activation.