Investigations of Dinitrogen Fixation via an N2 Cleavage Pathway

The industrial fixation of dinitrogen (N2) to ammonia (NH¬3) is critical to the production of synthetic fertilizer and currently supports the food supply of over 50% of the world’s population. However, this vital process consumes ca. 2% of all global energy each year and produces a similarly large amount of CO2 due to its reliance on fossil fuels and centralized high pressure reactors. Chapter 1 details how an electrochemical approach would be economically and environmentally desirable and discusses how recent advances in homogeneous N2 fixation catalysts could best be translated to electrocatalysis. Chapter 2 identifies the products of electroreduction of a Ru(NH3) species, identifying a number of N2-containing products and also highlights how modifying a ligand backbone influences activation of N2 ligands. Chapter 3 reports the reactivity of (PONOP)Re complexes, revealing that halide dissociation can effectively gate N2 coordination and also that coordination number and geometry are extremely important in both thermal and photochemical N2 cleavage. Chapters 4 and 5 explore how these principles can be translated to (pincer)Mo systems, demonstrating electroreductive N2 cleavage at Mo for the first time. Mechanistic investigations of (pyPNP)MoBr3 revealed key differences between chemical and electrochemical processes, while studies of (PSP)MoX3 (X = Cl, Br) demonstrated the impact of halide identity on product formation. In Chapters 6 and 7, a new phosphinite pincer ligand is developed for its unique chelating ring size and its reactivity with NiII and Ni0 precursors is explored. Of note, an unanticipated P–O bond oxidative addition reaction with a Ni0 precursor was observed, which may assist in development of both new methodologies for phosphine synthesis as well as ligand design principles for future phosphinite ligands to improve stability. Finally, in Chapter 8, the impact of temperature on hydricity was measured for the first time and used to rationalize trends in CO2 hydrogenation catalysis.Doctor of Philosoph