In this project funded by the Chemical Synthesis Program of the Chemistry Division, Professor Alan Heyduk of the Department of Chemistry at the University of California, Irvine will develop the early transition metal chemistry of redox-active, pincer ligands. Redox-active ligands provide a method for facilitating multi-electron reactivity at metal centers that are traditionally incapable of redox reactivity. Professor Heyduk's research effort will focus on understanding the impact of metal choice and ligand substituent on both the redox properties of these novel ligands as well as the capacity for small molecule activation at the metal center. Systematic synthesis of ligand derivatives will be complemented by detailed spectroscopic, electrochemical, and computational studies to developing a deeper understanding of the electronic interactions between redox-active ligands and coordinated metal ions.
The proposed work could lead to new homogeneous catalysts for small molecule reactions such as water oxidation, hydrogen production and C-H bond functionalization. Success in the former two areas could impact energy storage strategies for alternative energy solutions such as solar and wind. Success in C-H bond functionalization would have an impact on any area of chemical synthesis in which it is desirable to utilize low-cost, readily abundant chemical feedstock in an atom-economical way. The proposed work will also provide training in both fundamental chemical sciences and in next-generation alternative energy chemistry to the next generation of scientists.
The discovery of energy efficient catalysts for small-molecule reactions has driven research into coordination complexes of the transition metals. Small-molecule activation reactions include nitrogen reduction for fertilizer production, carbon dioxide reduction and hydrogen production for alternatives to fossil fuels, and oxygen activation for environmentally-friendly chemical transformations. These reaction types all require multi-electron reactivity and often times the catalysts designed to promote these reactions rely on rare precious metals such as rhodium, iridium, palladium and platinum. This NSF-funded project targeted a different approach to the development of catalysts for small-molecule activation reactions: one that incorporates inexpensive and abundant metals in tandem with redox-active ligands. In this approach, the redox-active ligands are used to facilitate multi-electron reactivity at metals that normally cannot promote such reactions. During the tenure of this award, a new catalyst was developed for the activation of O2 gas and transfer of the oxygen atoms to organic substrates: a key proof-of-concept reaction for developing benign and inexpensive catalysts for large-scale chemical oxidation reactions that normally require toxic and expensive reagents. At the core of these studies has been an effort to understand fundamental aspects of chemical reactivity so that new paradigms could be developed and the lessons learned could be broadly applied to many problems in catalysis. Indeed, work initiated in this NSF funding cycle has led to the identification of new potential catalysts for water oxidation and proton reduction (the two key reactions in artifical photosynthesis). In addition to these scientific breakthroughs, NSF funding has resulted in training of two graduate students, three undergraduate researchers and one postdoctoral researcher.
