CAREER: SusChEM: Development of Manganese Hydrosilylation Catalysts for Silicone Curing

Arizona State University, Scottsdale AZ

Investigators

Abstract

In this project funded by the Chemical Catalysis Program of the Chemistry Division, Professor Ryan Trovitch of Arizona State University is studying ways to make catalysts from abundant metals, such as manganese, that can be used to prepare silicone polymers. Polymers are long chain molecules that derive many of their properties from the entanglements and interactions between the chains. Polymers have become ubiquitous materials in our daily lives, impacting most industries, including agriculture and food, health and safety, as well as transportation. For more than half a century, silicone polymers have been used in a variety of consumer products including contact lenses, flexible tubing, and medical implants. Most catalysts that are widely employed in silicone preparation and curing are based on precious metals such as platinum or iridium, relatively toxic elements that are costly to obtain due to their low abundance in the Earth's crust. The development of manganese-based catalysts for silicone preparation would have the potential to supplant precious metal catalyst use, which would represent a significant advance in sustainable chemistry. Professor Trovitch is also working to enhance student and public familiarity with green chemistry. He is developing a sustainability workshop for local high school students, and videos based upon this program will be made available to achieve broad dissemination. As an Advisory Board Member of the Green Chemistry Commitment, he is participating in ongoing initiatives to introduce undergraduate and graduate students to advanced topics in sustainable chemistry through updated coursework and laboratory experiences. Professor Trovitch is also organizing Science Cafe discussions in collaboration with the Phoenix Public Library. In this project, Prof. Ryan J. Trovitch of Arizona State University is developing sustainable manganese hydrosilylation catalysts that will exhibit comparable activity and selectivity to widely used precious metal catalysts. Relative to second and third row transition metals, manganese remains underutilized in catalytic applications due to its propensity to participate in one-electron reaction pathways. Recent results have shown that polydentate, redox non-innocent chelate ligands enable manganese-catalyzed carbonyl hydrosilylation by reversibly transferring electrons and partially dissociating throughout catalysis. Building on this discovery, Professor Trovitch is studying several aspects of manganese-catalyzed hydrosilylation reactions including manganese olefin hydrosilylation catalysts that can serve as replacements for ones based upon platinum, novel carbonyl hydrosilylation pathways to crosslink polyones with polyhydrosilanes or polyhydrosiloxanes, and dehydrogenative silylation pathways to the synthesis of siloxane networks. Via electronic structure determinations and mechanistic studies, highly active manganese catalysts for olefin hydrosilylation, carbonyl hydrosilylation, and dehydrogenative silylation are being developed by judiciously modifying their ligand frameworks. Successful completion of this project will transform current knowledge of manganese catalysis while revealing potential advantages of high-denticity redox non-innocent chelate utilization.