CAREER: Terminal Hydride Complexes of High-spin Fe and Mn

With the support of the Chemical Synthesis (SYN) program in the Division of Chemistry, Professor Alex McSkimming of Tulane University is studying synthetic molecules relevant to the Earth’s nitrogen cycle. Conversion of atmospheric dinitrogen into bioavailable ammonia by microorganisms, a process known as nitrogen fixation, is essential for the sustenance of plant life on this planet. This reaction is mediated by the ‘iron-molybdenum cofactor’, or ‘FeMoco’, which resides within these organisms, and enables breaking of the remarkably strong dinitrogen triple bond. A paradigm shift came this century with the realization that nitrogen fixation at FeMoco occurs via intermediates containing iron-hydrogen bonds; i.e. iron hydrides. Through the study of model chemical systems, the proposed research will shed light on this important and unusual class of molecules. This, in turn, will further scientific understanding of biological systems critical to human health and development. As ammonia is a potential alternative fuel, an improved knowledge of FeMoco is also expected to lead to further advancements in renewable energy technology. This research project will be integrated into an education/outreach program aiming to improve the participation of high school students in STEM. A key distinction of hydride-bound FeMoco states is that the iron hydride sites are—in contrast to the vast majority of all other metal hydrides—projected to be locally high-spin. This spin state is expected to profoundly impact the bonding, spectroscopy and reactivity of such species. Nevertheless, high-spin hydride complexes, particularly those for which the hydride is terminally bound, remain rare, and their properties only poorly understood. This research project therefore aims to prepare and study new terminal hydride complexes of manganese and iron, particularly those with electron counts pertinent to FeMoco. Molecules with unusual oxidation states and/or unprecedented hydride binding modes with be particular targets. This proposal also seeks to explore the reaction chemistry of high-spin hydride complexes with unsaturated small molecule FeMoco substrates. 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.