Inorganic Chemistry Seminar: Professor Neil Tomson, University of Pennsylvania
"Ligand Flexibility in Surface-Inspired Cluster Chemistry"
Host: Hemamala Karunadasa
About the Seminar
Metallic surfaces perform many chemical transformations that hold promise for the future energy economy, including N2 reduction, NH3 oxidation, and alkane synthesis, but surfaces are difficult to tune, limiting chemists’ ability to improve their efficiencies. Molecular cluster complexes inspired by surface chemistry have been studied for decades as a way to capitalize on the advantages of metallic surfaces while avoiding the scaling relationships that govern their activities. Progress in this area has been hampered, however, by the lack of ligand architectures able to provide an appropriate degree of geometric and electronic flexibility to the cluster core.
This talk will describe our use of macrocyclic, multi-nucleating ligands that have been designed to bind small metal clusters (2‑4 metal atoms) in a way that mimics M–M bonding. Doing so allows for both facile electron redistribution within the cluster-ligand assembly and a high density of thermally accessible electronic states. These ligands have the added advantage of providing the geometric flexibility needed for stabilizing a range of surface-relevant species. Examples include diiron dinitrogen complexes that exist in a geometry reminiscent of the side-on binding of N2 to the Mittasch catalyst, a diiron-supported sp‑hybridized bridging nitride that converts into an sp3‑hybridized bridging amide following hydrogen atom transfer, and the first (putative) dicobalt bridging nitride – a highly reactive species that mimics aspects of surface nitrides that develop during NH3 oxidation in the Ostwald Process. Particular attention will be paid to the electronic structure of the electrophilic diiron bridging nitrides, which appears to exhibit a sub-valent oxidation state. Finally, this talk will describe our recent observation of a diiron system that is competent for performing the unassisted oxidative addition of C–C σ-bonds. Subsequent functionalization chemistry results in full synthetic cycles and paves the way toward catalytic C–C σ-bond metathesis.
About the Speaker
Neil Tomson received a B.A. in Chemistry, with honors, in 2004 from Grinnell College, where he worked for Prof. T. Andrew Mobley on transition metal stannyl complexes, then a Ph.D. in 2009 from the University of California, Berkeley, where he investigated Group 5 imido chemistry under the joint supervision of Profs John Arnold and Robert G. Bergman. He held a post-doctoral position at the Max Planck Institute for Bioinorganic Chemistry (now Chemical Energy Conversion) under the direction of Prof. Dr. Karl Wieghardt that focused on the physical inorganic and computational investigation of redox-activity in 3d metal nitrosyl and nitrosoarene complexes. Neil then taught for a year at the College of St. Benedict | St. John’s University before moving to Los Alamos National Laboratory, where he worked on uranium imido chemistry as a post-doctoral researcher in Prof. James M Boncella’s laboratory. He joined the faculty at the University of Pennsylvania as an assistant professor in 2015. His awards include Glenn T. Seaborg and Director's Post-doctoral Fellowships at LANL, an NIH Maximizing Investigators’ Research Award (MIRA) for Early-Stage Investigators, and an NSF CAREER Award.