CHE 598 Seminar: Hydrogenation of carbon dioxide to formate by a series of Rh-bis (diphosphine) molecular catalysts and artificial metalloenzymes
About the event
Presenter: Dr. Joseph Laureanti, Staff Scientist, Pacific Northwest National Laboratory
Dr. Laureanti received his B.S. (2012) in Biochemistry and Ph.D. (2017) in Biochemistry from Arizona State University. During his Ph.D. studies he was funded by a National Science Foundation program, Integrative Graduate Education and Research Traineeship (IGERT-SUN) focused on solar energy utilization. He joined the Pacific Northwest National Laboratory (PNNL) in 2017 as a post-doctoral research assistant, focusing on investigation of outer coordination sphere effects on molecular catalysts that store energy in chemical bonds and the design of artificial metalloenzymes. He became a staff scientist at PNNL in 2019. His research interests include studies of energy relevant chemistries with emphasis on the design of transition-metal based molecular catalysts and artificial metalloenzymes for CO2 activation. He also focuses on developing virtual reality tools for research and teaching applications.
ABSTRACT:
Energy storage and implementation of an efficient renewable energy infrastructure is one of the most important scientific challenges we face. Our group focuses on storing electrons derived from renewable resources, such as H2, in chemical bonds of organic molecules. We are also interested in extracting knowledge from enzymes, which do this process, very efficiently, and implementing these features, in a controlled manner in an artificial metalloenzyme. Formic acid, derived from CO2 hydrogenation, is an attractive liquid fuel due to the high energy density and facile transportation processes in comparison to H2 gas. Effective CO2 hydrogenation catalysts are facilitated by efficient interactions between the hydride donor (metal-hydride), and the substrate (CO2).
In this work, I will present both our efforts to understand the series of Rh-bis (diphosphine) based molecular catalysts, as well as metalloenzyme’s, that utilize the same molecular catalyst as an active site. We investigated a series of molecular complexes in organic solvent, THF, using [Rh‑(PNXP)2]+, where X represents various amino acids or amino acid analogues. For our molecular systems, which only operate in organic solvent, a strong base (Verkade’s base) is required as a proton acceptor, and amino acid ester analogues serve as the outer-coordination sphere component. The artificial metalloenzyme is catalytically active in water, where the molecular complex alone is not. The outer-coordination sphere is represented by a protein scaffold (LmrR) and water or bicarbonate are presumed to act as the requisite base. We also produced a series of artificial metalloenzymes using single, double, and triple point mutations to investigate the impact that outer-coordination sphere interactions can impose on catalytic activity in an aqueous medium, successfully increasing activity up to 4-fold. In both systems, high pressure operando NMR spectroscopy is utilized to measure in situ formate production. On average, catalysis in organic solvent operates at a rate two orders of magnitude faster than the aqueous systems, with a concomitant rearrangement of the catalytic cycle when moving from organic solvent to an aqueous medium.