Excited State Reactivity of Metal-Ligand Multiple Bonds for Ammonia Production and Hydrocarbon Functionalization

Author

Victoria Z. Valley, Louisiana State UniversityFollow

Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

Ammonia (NH₃) is a crucial compound that is an essential component to agriculture. The enzyme nitrogenase utilizes ATP as a natural energy source for nitrogen fixation, while the contrasting Haber-Bosch Process requires energy-intensive and extreme conditions. The high energy demands of the Haber-Bosch Process leads to the consumption of about 1-2% of the world’s energy and produces 175 million metric tons of NH₃ per year. Although the Haber-Bosch Process consumes massive amounts of energy, there is currently no other large-scale ammonia production technique.

New approaches to nitrogen fixation have been proposed that utilize transition metal complexes under more inert conditions. Light can be used to generate excited electronic states of the metal nitride with destabilized M–N bonds and allow for further reactivity to take place. Some rhenium nitrides supported by chelating bisphosphines, such as [ReN(dppe)₂Cl]Cl, have been reported to be photoactive upon irradiation with visible light. These nitride complexes can be used to probe the conditions necessary to reduce terminal nitrides and characterize the nitrogen-containing products. The light-enhanced reactivity of ammonium formation is explored with a variety of acids. The monocationic species acts as a light absorber to perform net chemistry and ultimately produce ammonium.

Like the Haber-Bosch Process, the industrial procedure for C–H activation utilizes high temperatures and pressures to overcome the kinetic and thermodynamic barrier. Light hydrocarbons are a cheap and abundant feedstock which can be functionalized to form more valuable products.Industrially, the process of converting these hydrocarbons to other materials is inefficient due to the kinetic challenge of activating C–H bonds. Determining a cost-effective and efficient method for C–H bond functionalization is of great interest so these cheap feedstocks can be utilized to produce more valuable products. Comparing the basicity of well-known photocatalysts to MoO₂Cl₂(bpy-^tBu) could shed light on how the structure affects the overall activity and ability to functionalize hydrocarbons.

Date

10-29-2024

Recommended Citation

Valley, Victoria Z., "Excited State Reactivity of Metal-Ligand Multiple Bonds for Ammonia Production and Hydrocarbon Functionalization" (2024). LSU Doctoral Dissertations. 6605.
https://repository.lsu.edu/gradschool_dissertations/6605

Committee Chair

Chambers, Matthew