High Turnover Frequency Earth-Abundant Metal Catalysis

Our laboratory has focused on the development of ligand platforms that support substrate coordination and activation at low-valent first row transition metals. This interest has allowed for the preparation of a manganese catalyst that mediates carbonyl hydrosilylation with turnover frequencies of up to 4,900 min-1 in the absence of solvent. Although this compound is inactive for alkene reduction, mechanistic insight guided the development of a second catalyst that has been found to cure silicones in the presence of polymethylhydrosiloxane, a reaction that typically requires the use of platinum catalysts. These observations led us to study the dehydrocoupling of silanes and amines, an approach to Si-N bond formation that offers hydrogen as a value-added byproduct. This methodology is a sustainable alternative to traditional aminosilane synthesis, which utilizes corrosive chlorosilanes and generates one equivalent of ammonium salt waste for each Si-N bond that is formed. We recently discovered that our well-defined manganese hydride catalyst is capable of coupling silane (SiH4) to primary and secondary amines to generate atomic layer deposition precursors for silicon nitride. This catalyst has more recently been found to dehydrocouple ammonia with silanes to generate perhydropolysilazane and organic polysilazanes, reagents that are used to protect semiconductor and automobile surfaces, respectively. The coupling of silanes with diamines has also allowed for the preparation of crosslinked preceramic materials. Notably, Si-N dehydrocoupling activities of greater than 100 s-1 have been observed for two different Earth-abundant metal catalysts developed at Arizona State University, and our efforts to optimize alkene, alkyne, and nitrile hydrofunctionalization turnover will be summarized.

Speaker: Ryan Trovitch, Arizona State University