CAS: Elucidating Trends in Earth-Abundant Metal Catalyzed Dehydrocoupling

CAS: Elucidating Trends in Earth-Abundant Metal Catalyzed Dehydrocoupling CAS: Elucidating Trends in Earth-Abundant Metal Catalyzed Dehydrocoupling Overview Although significant progress has been made in the development of highly-effective and robust Earth-abundant metal catalysts over the last 20 years, few projects have sought to identify electronic structure trends that underlie and inform the catalytic activity of structurally-related compounds. This project will evaluate the ability of newly-synthesized manganese, iron, cobalt, and nickel catalysts to mediate the dehydrogenative coupling of main group hydride pairs while simultaneously advancing underappreciated and underdeveloped applications in inorganic catalysis. The dehydrogenative coupling of amines to silanes is a transformation of particular interest since it can allow for the sustainable and atom-efficient production of reagents that are critical to semiconductor manufacturing. For example, the coupling of secondary amines to silane can yield volatile aminosilanes that are used to deposit silicon nitride or silicon carbonitride layers onto semiconducting surfaces. Alternatively, N-Si dehydrocoupling can generate perhydropolysilazane from ammonia and silane, a synthetic pathway that avoids the stoichiometric formation of ammonium salt waste while facilitating purification. Polycarbosilanes prepared in this way are promising anti-corrosion and anti-graffiti coatings for surfaces that are common to the construction and transportation sectors. The dehydrogenative coupling of other main group hydrides can offer a convenient way to prepare chemical vapor deposition precursors, quantum dot synthons, or silylborane reductants. The catalysts developed in this project may also be used to catalyze main group bond forming reactions that have not been previously achieved. The broader impacts of this proposal will extend to the support of underrepresented minority students, the development of a research-driven undergraduate laboratory experiment, and the creation of a manual for sustainable general and inorganic chemistry. Intellectual Merit To design highly-effective base metal catalysts for the heterodehydrocoupling of main group hydrides, this project will rely on physical inorganic techniques to elucidate electronic structure factors that contribute to catalytic performance. Trends in electron count, metal oxidation state, geometry, chelate coordination, and ligand redox activity are likely to influence the rate at which catalysts mediate dehydrocoupling, information that can be used to inform the design of improved catalysts. Preliminary studies have revealed that anionic chelates can support promising base metal N-Si dehydrocoupling activity; therefore, we will prepare series of phosphorous-substituted arene diimine manganese, iron, cobalt, and nickel compounds in Specific Aim #1. Arene diimine ligands are an anionic analog of well-studied pyridine diimine ligands, and their electronic properties and modularity will be fully explored in this effort. In Specific Aim #2, we will evaluate the ability of arene diimine first row metal catalysts to dehydrocouple amines and silanes to prepare value-added monomers, perhydropolysilazane, and polycarbosilazane coatings. In Specific Aim #3, our most effective dehydrocoupling catalysts will be used to prepare chemical vapor deposition and atomic layer deposition precursors that feature N-Ge, N-Al, and Ga-P bonds, quantum dot synthons that feature P-Si and P-Ge bonds, and reductive functionalization reagents that feature B-Si and Al-Si bonds. Overall, this project has the potential to expand the known scope of main-group element dehydrocoupling and elucidate halogen-free synthetic pathways that can be used to prepare versatile main group reagents. Broader Impacts There are several ways in which the goals of this project can result in positive societal outcomes. The PI will expand access to underrepresented minority students through mentorship and synthetic training, participate in events hosted by the Western Alliance to Expand Students Opportunities, and reach out to foundations and universities to encourage Hispanic undergraduates to pursue graduate research. One of the research objectives targeted in this project will be tested by ASU undergraduates to offer them exploratory chemical research experience and teach them how to evaluate the relative sustainability of competing synthetic transformations. In addition to preparing a laboratory manual on these topics for ASU students, the PI will work with Beyond Benign and faculty members throughout the country to develop a sustainable general and inorganic chemistry laboratory guide for post-secondary educators. Where possible, efforts will be made to distribute effective base metal catalysts to members of the synthetic community.