Klaus H. Theopold, Professor
University of Delaware
214 Lammot DuPont Laboratory
Newark, DE 19716
Universität Hamburg, Vordiplom, May 1977; University of California, Berkeley, Ph.D. (Inorganic Chemistry), 1982
Catalytic processes, such as the coordination polymerization of small olefins and the oxygenation of hydrocarbons motivate our preparative and mechanistic work with transition metals. Our approach involves the synthesis of 'unusual' molecules (by virtue of their oxidation state, spin state, electronic configuration, molecular structure, reactivity, etc.), their full characterization with various spectroscopies and other suitable physical techniques (i.e. electrochemistry, magnetic susceptibility measurements, X-ray crystallography), and finally, the elucidation of their reactivity with organic or inorganic substrates..
Based on the notion that open shell organometallics—i.e. 'metallaradicals' —will exhibit novel reaction patterns, we are exploring the chemistry of paramagnetic chromium alkyls. Organometallic complexes containing chromium in oxidation states ranging from +I to +VI, and deviating to various degrees from the expected 18- electron configuration, have been prepared in our laboratory. Much of this work as been directed at preparing homogeneous chromium catalysts for the polymerization and oligomerization of olefins. These compounds serve as models for industrially used heterogeneous catalysts, which have eluded molecular level understanding for nearly half a century. Our catalysts, on the other hand, can be fully characterized. Systematic variation of the ligands, formal oxidation state, charge, etc. creates a fundamental understanding of the factors governing catalytic activity and thus a conceptual framework for the development of improved catalysts.
Our focus on open-shell compounds has also led to the discovery of polynuclear metal complexes with a variety of interesting magnetic interactions. Magnetochemical studies are the basis for the design of 'molecular magnets' and we carry out magnetic measurements whenever warranted.
Another current project focuses on the activation of dioxygen (O2) and other readily available oxidants with transition metal catalysts. Catalytic oxidations are among the most important chemical transformations and the use of O2 as a terminal oxidant is an important goal of 'green' chemistry. We are taking advantage of the unique steric characteristics of highly substituted tris(pyrazolyl) borate ligands in stabilizing coordination compounds of small inorganic ligands. Binding of O2 to a metal, followed by cleavage of the O-O bond, generates metal oxo groups, which are highly reactive. For example, they can abstract hydrogen atoms from saturated alkyl groups. The selective functionalization of unactivated alkanes is one of the long-term goals of this work.
The studies carried out in this research group involve a mixture of chemical synthesis, physical measurements, and mechanistic investigations designed to give students a broad set of skills to apply in any future employment setting.
- K. A. Kreisel, G. P. A. Yap and K. H. Theopold "Synthesis, Characterization and Electronic Structure of Diimine Complexes of Chromium," Inorg. Chem.47
- K. A. Kreisel, G. P. A. Yap, O. Dmitrenko, C. R. Landis and K. H. Theopold "The Shortest Metal-Metal Bond Yet – Molecular and Electronic Structure of a Dinuclear Chromium Diazadiene Complex," J. Am. Chem. Soc.129
- W. H. Monillas, G. P. A. Yap and K. H. Theopold "A Tale of Two Isomers - a Stable Phenyl Hydride and a High Spin (S=3) Benzene Complex of Chromium," Angew. Chem. Int. Ed.46
- W. H. Monillas, G. P. A. Yap, L. A. MacAdams and K. H. Theopold "Binding and Activation of Small Molecules by Three-coordinate Cr(I)," J. Am. Chem. Soc.129
- L. A. MacAdams, G. P. Buffone, C. D. Incarvito, A. L. Rheingold and K. H. Theopold "A chromium catalyst for the polymerization of ethylene as a homogeneous model system for the Phillips catalyst," J. Am. Chem. Soc.127
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