RII Track-4: Pulse Radiolysis Studies of H2 Generation by [Cp*Rh] Complexes to Characterize Design Rules for Improved Catalysts

University Of Kansas Center For Research Inc, Lawrence KS

Investigators

Abstract

Nontechnical Description Renewable energy sources, which provide power without routine emission of pollutants, are being developed rapidly in the United States and elsewhere. However, effective and practical methods for the direct generation of useful chemicals using renewable energy remain elusive. In part, this challenge arises from a lack of detailed and predictive information on the individual steps involved in energy-storing chemical reactions such as hydrogen generation or carbon dioxide conversion. With the support of an EPSCoR Research Fellowship, the PI will conduct research at Brookhaven National Laboratory (BNL), where he and his collaborators will focus on revealing the detailed features of selected energy-storing reactions as they proceed step-by-step. Unique resources available at BNL, including techniques that can monitor reactions in real time as they occur, will be used to conduct studies of active materials developed in the PI?s laboratory at the University of Kansas. Within the framework of this research, the PI and his students will closely collaborate with scientists in the BNL Artificial Photosynthesis group, fostering a strong partnership between institutions that will enable mutually beneficial exchange of knowledge and expertise while also accelerating research progress. More broadly, this effort will further scientific workforce development in Kansas by providing opportunities for enhanced training and dissemination of research findings in local and regional forums. Technical Description The research effort of this fellowship focuses on experimental study of mechanisms of proton and electron management in reductive molecular catalysis. Proton/electron management is important in artificial photosynthetic systems that can be used to generate energy-dense chemicals and fuels; in such systems, water serves as a sacrificial reagent to provide reducing equivalents to catalysts that mediate formation of reduced products. A group of [Cp*Rh]-based molecular catalysts (Cp* = pentamethylcyclopentadienyl; Rh = rhodium) developed in the PI?s laboratory are the target of the studies in this project, as they are highly active for catalysis, recyclable, and built from commonly available components. However, unexpected metal- and ligand-centered protonation events have recently been implicated in the activity of these compounds, motivating detailed studies aimed at revealing the features of their structure and bonding that favor efficient catalysis. On-site experimental work at BNL will focus on pulse radiolysis and time-resolved UV-visible and infrared spectroscopic studies in order to generate and observe the transient intermediates involved in catalysis, with the goal of elucidating the roles of specific protonation sites, metal hydride species, and ancillary redox-active ligands. Complexes that feature a variety of ligand environments will be studied, including model compounds that complement the active catalysts. The outcomes of this research include fundamental knowledge for rational design of improved molecular catalysts, particularly systems with ligand environments built upon cyclopentadienyl-type ligands that may function as unconventional proton relays. Notably, the design rules developed here could be broadly useful, as cyclopentadienyl ligands are ubiquitous in organometallic chemistry and catalysis, and are commonly used in industry. 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.