Our research involves the synthesis and characterization of new inorganic complexes and materials. The long-term goal of our laboratory is to improve the understanding of actinide and transition-metal coordination chemistry by synthesizing difficult-to-obtain complexes and studying their bonding and reactivity. A parallel goal, related to the first, is to determine what extent the f orbitals participate in bonding. We are also trying to discover new transformations mediated by metal centers; specifically reactions catalyzed by transition-metal nitrosyl cations.

Uranium-Ligand Multiple Bonds. Aside from the practical applications of studying actinide coordination chemistry, important questions about actinide-ligand bonding remain, specifically in regards to the actinides ability to form covalent multiple-bonds, and the participation of the 5f orbitals in those interactions. A major part of our research program focuses on the synthesis and characterization of new high- and mid-valent uranium alkoxide complexes (see photo below), and the exploration of their bonding and reactivity, for the purpose of answering these important questions.

We have isolated a series of homoleptic uranium hexakis(tert-butoxide) complexes that differ only in oxidation state. These complexes have proven to be excellent starting materials, and are easily elaborated. We plan to use these complexes as precursors to uranium oxo, sulfido, and nitrido complexes. Because the synthetic methods usually used to introduce multiply-bonded ligands into a metal’s coordination sphere do not work for the actinides, we are developing new strategies to generate these interesting materials.

Synthesis and Reactivity of Uranyl(V).  Uranyl(V) or UO₂⁺ is a rare analogue of the much better understood uranyl(VI) ion.  This complex is of interest because of its intermediacy in the photochemical reactivity of uranyl(VI) and also because of its similarity to neptunyl(V) (NpO₂⁺), a component of spent nuclear fuel which has proven to be difficult to extract using the current technologies.  The chemistry of uranyl(V) has not been extensively explored because of the difficulty of isolating this fragment, and we are currently studying the ability of the b-diketiminate class of ligands (also known as nacnac) to stabilize this molecule.  We have recently isolated one example of a uranyl(V) complex, where the uranium is coordinated by one nacnac ligand and two phosphine oxide ligands, and are currently exploring its reactivity.



Transition-Metal Nitrosyl Complexes. Our other area of interest is the synthesis and characterization of transition-metal nitrosyl cations, a relatively rare class of compounds. By studying these complexes we hope to enhance our understanding of the interaction between metal ions and strongly p-acidic ligands. In addition, we will investigate the ability of these molecules to effect the electrophilic C-H activation of alkanes. Metal cations, such as Hg²⁺, Pd²⁺ and Pt²⁺, dissolved in electrophilic media like sulfuric acid are known to catalyze the selective oxidation of alkanes. Interestingly, nitric oxide (NO) can bind to several different metal ions under these conditions, forming stable metal nitrosyl cations. Considering the electron-withdrawing nature of the NO ligand, it is possible that these nitrosyl complexes may be capable of similar electrophilic C-H bond activation as observed in the Hg, Pd, and Pt systems. However, in order to find a metal nitrosyl cation that is a viable catalyst we are studying the synthesis, structure and chemistry of these molecules.

Reactivity of Uranium(III) Hydride.  We are also exploring the reactivity of uranium(III) hydride.  This unique material is of interest as a potential nuclear fuel, however its basic coordination chemistry is not well understood.  We have found that this compound vigorously reacts with mild oxidants to generate a variety of useful uranium(III) and uranium(IV) synthons in good yield.  This work was featured on the inside cover of Dalton Transactions issue 44 (2008).