NSF Award
2400019
With support from the Chemical Catalysis Program of the Division of Chemistry, Professor Seth Brown and his research team of the University of Notre Dame will study the factors that enable the preparation and stabilization of metal ligand multiple bonds. While all atoms in chemical compounds are held together by bonds, not all bonds are created equal. Some bonds, such as carbon-oxygen bonds, are strong and found everywhere in Nature. Others, including multiple bonds between late transition metals such as iridium and oxygen or nitrogen atoms, so-called iridium-oxo or -nitrido bonds, are rare. They are interesting both because of their scarcity and because they are likely to be reactive enough to be useful in forming new chemical bonds and thus acting as catalysts or reagents to promote cleaner and more efficient preparation of useful substances. The working hypothesis underpinning these studies is that the metal-nitrogen bonds may be more stable than previously believed, with the difficulty being in finding ways to prepare them. In contrast, the metal-oxygen bonds may only be stable if the iridium atoms have other designed groups surrounding them. Dr. Brown will also work to develop new materials and approaches to help teach chemical principles about the rates of reactions (chemical kinetics) in ways that will be accessible and engaging to a wide audience. This will include developing experiments that can be conducted with readily available household materials, and working out ways to measure color changes over time using cell phone cameras.<br/><br/>In this project, Professor Seth Brown and his team at Notre Dame will develop synthetic approaches to terminal oxo and nitrido complexes of late transition metals such as iridium. Such compounds are rare, and in tetragonal (octahedral or square pyramidal) environments unknown, due to the so-called “oxo wall” originating in their high d electron count in accessible oxidation states. The hypothesis that iridium nitrides will actually be sufficiently stabilized by the nitrido ligand to exist in the +7 oxidation state, heretofore deemed inaccessible, will be pursued using ancillary ligands that are either redox-active, allowing the iridium to jump from a common iridium(III) oxidation state (iminoxolenes, calix[4]pyrrolides) or ones that stabilize an uncommon iridium(V) precursor (alkyls or aryls). Oxo compounds will be sought using iminoxolene or dioxolene ligands capable of electronic stabilization of the oxoiridium moiety. Any oxo or nitrido compounds that can be generated will be subjected to physical characterization to illuminate their bonding, and their reactivity with organic substrates will be analyzed to see how the novel electronic structures can be used to effect useful oxidations.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
