High-Valent Metal-Oxo Species: Beyond the Oxo Wall

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With funding from the Chemical Structure, Dynamics and Mechanisms B Program of the NSF Chemistry Division, the collaborative research team of Professor Lehnert of University of Michigan and Professor Shearer of Trinity University investigates different Cobalt- and Nickel-based oxo complexes to improve the understanding of the structural and electronic properties of these unstable species. Metal-oxo species are often implicated in enzymatic and synthetic catalysis and play key roles in hormone biosynthesis, drug metabolism, and in photosynthesis. In the chemical and pharmaceutical industry, reactive metal-oxo complexes are used as catalysts for the production of chemical feedstocks and in the synthesis of fine chemicals and pharmaceuticals. Currently, scientists are lacking a detailed understanding of the properties of late-transition metal oxo species, which show great potential for applications in chemical catalysis, but which are underutilized as scientists cannot control their reactivity well. Professor Lehnert is the director of the D-RISE program, which provides 7-weeks, full-time summer research opportunities to high school students from Detroit that belong to underrepresented minority (URM) groups in science, technology, engineering and math (STEM) disciplines. The activities include funding for one high school student to participate in D-RISE. Professor Shearer conducts research exclusively with undergraduate students recruited through mechanisms that aim at increasing the participation of URM students in the sciences (in particular, Trinity University's McNair Scholar's program). Professor Lehnert and Professor Shearer are developing an understanding of the structural and electronic properties of a number of high-valent Co- and Nickel-oxo complexes. Especially the effect of the spin state on the electronic properties of these complexes is underappreciated; yet, as demonstrated for iron-oxo complexes, the spin state has a pivotal influence on the reactivity of these species. In the case of Co-oxo complexes, spin state also provides a potential pathway for a true violation of the "oxo wall", a concept that is considered a holy grail in high-valent metal-oxo chemistry. Another important dichotomy of metal-oxo complexes is the question of whether they are best represented as metal-oxo or metal-oxyl species, and how this influences their reactivity. Therefore, the research on the fundamental properties of high-valent Co- and Nickel-oxo complexes addresses many important fundamental questions about high-valent metal-oxo complexes with general (conceptual) implications for this area of research. The proposed research has broad implications with respect to further developing late first-row transition metal catalysts for water oxidation and the functionalization of organic molecules. In particular, bioinspired catalysts for the functionalization of organic molecules are highly sought after as industrial catalysts for the production of chemical feedstocks and pharmaceuticals. This project employs a large array of spectroscopic and theoretical methods, including electron paramagnetic resonance, magnetic circular dichroism, resonance Raman, and X-ray absorption spectroscopy. Theoretical methods (density functional theory and multi-reference quantum-chemical calculations) are used to interrogate the spectroscopic results, and connect them to electronic structure and reactivity. Professor Lehnert is actively engaged in STEM outreach programs focused on recruiting underrepresented minority (URM) high school students from Detroit to STEM fields. Professor Shearer's laboratory works exclusively with undergraduate (UG) students, which are recruited through mechanisms that aim at increasing the participation of URM UG students in the sciences (in particular, Trinity University's McNair Scholar's program). Both of these activities support the broader impacts of the project.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.