This award in the Chemical Synthesis (SYN) program supports work by Professor Trevor W. Hayton at the University of California Santa Barbara to carry out fundamental studies on the synthesis and reactivity of metal ions in their highest oxidation states. Often complexes in high oxidation states are too reactive to isolate, making their characterization and study a significant challenge. Thus we are trying new approaches, both in terms of ligand design and synthetic methodologies, to advance the chemistry of high valent metal ions. Specifically, we are developing strongly electron donating ligands, such as the ketimide ligand, which are capable of stabilizing these oxidation states. In a similar vein, we are developing new, broadly applicable synthetic routes for generating metal-ligand multiple bonds. To realize this latter goal we are utilizing the protection/deprotection methodology to access these novel functional groups.
The basic research funded by this award will advance the synthetic manipulation of high oxidation state materials and provide a greater understanding of the reactivity of ions. Many of these ions, in particular, manganese and iron, have potential applications in catalysis and artificial photosynthesis, and the information we acquire will be used in efforts to alleviate our growing energy shortage.
The central goal of this project was the synthesis and study of high oxidation state metal ketimide complexes. High valent metal centers, such as Mn(IV), Fe(IV), and Co(IV), are important intermediates in many organic transformations and industrial processes, and by exploring the fundamental properties of these ions we can provide new insights and understanding into these important reactions. In addition, these metals are cheap and abundant, in comparison to precious metals, such as palladium, platinum, and rhodium, making them attractive alternatives for catalysis. One significant research accomplishment from this project is the synthesis of a rare Co(IV) coordination complex. Isolating a Co(IV) coordination complex allowed us to study the cobalt-ligand bonds in great detail. This work demonstrated that the ketimide ligand is a strong σ- and π-donor and also a good π-acceptor. Very few ligands feature this combination of orbital interactions, which establishes the uniqueness of the ketimide ligand, and suggests that the ketimide ligand may be able to promote unprecedented small molecule reactivity and catalysis. Another significant research accomplishment from this project is the demonstration of C-H activation by an N-oxyl radical-Lewis acid adduct. Demonstrating C-H activation is significant because expands the scope of known reactivity for N-oxyl radicals. As a result, our Lewis acid N-oxyl radical adducts could find use as catalysts for a wide breadth of oxidation reactions, including lignin depolymerization, which is a necessary first step in the development of lignin as a chemical precursor. The biopolymer lignin, an unwanted by-product of paper making, has the potential to be an important, renewable feedstock for the chemical industry, provided that efficient routes for its depolymerization can be found. Finally, during the award period, four graduate students, three undergraduate students, and one postdoctoral fellow participated in this project. They were trained in the synthesis and characterization of organometallic complexes, magnetism, and the safe handling of uranium and thorium. The number of junior researchers with combined training in these areas is small, and, as a result, they will be able to continue to make unique contributions to inorganic chemistry in the years to come. This training has also given my graduate students the marketability to pursue postdoctoral positions at top-tier institutions upon graduation from UCSB. Moreover, several of the undergraduates involved in this project have moved on to graduate school, where they continue to pursue chemistry research.
