Research Synopsis

Research in our group focuses on two main themes: i) chemical transformations at transition metal sites and ii) assembly of multinuclear metal sites as well as nanosized and extended structures.

Activation of Inert Molecules towards Atom-efficient Functionalization. We seek to develop new synthetic transformations that derive functionalized hydrocarbons from inexpensive and readily available resources. To this end, we will generate reactive transition metal complexes that can be used to activate small molecules and elements (including, but not limited to, CO₂, CO, NO, N₂O, N₂, H₂, S₈) for further reactions. New inorganic functional groups of late-transition metals and main-group elements will be targeted and will be used as synthons (transient or metastable) in reactions with organic substrates. These studies will be guided by systematic investigations of the structural and spectroscopic properties of the inorganic functional groups, providing insights into the electronic properties of the involved metal centers and metal-ligand interactions. The understanding of the properties of these functional groups on a fundamental level will in turn lay the foundation for interpreting and controlling their inherent chemical reactivity. Initially, we will focus on well-defined stoichiometric atom/group transfer cycles and ultimately attempt to develop catalytic cycles for the activation of elements and small molecules.

Biologically Relevant Multinuclear Metal Sites. Nature uses a wide variety of metalloenzymes to carry out bond activation and bond formation processes under mild conditions. The active sites of the enzymes hydrogenase, nitrogenase, and carbon monoxide dehydrogenase/acetyl-coenzyme A synthase, which are important components of the global cycling of hydrogen, nitrogen and carbon, consist of multinuclear metal centers; however, recent structure determinations by protein crystallography revealed unanticipated compositions of these metal sites. Thus, although the overall stoichiometry of the chemical reactions catalyzed by these enzymes had previously been established, detailed pictures of the mechanisms remain elusive. Our efforts in synthetic bioinorganic chemistry are directed at the preparation of multinuclear metal assemblies that serve as accurate structural models of the active sites, which then can be elaborated into functional models for the enzymic reactions. In order to gain more detailed insights into the mechanisms, we will attempt to identify and characterize reaction intermediates by spectroscopic means.

Functional Materials. Concepts of coordination chemistry and self-assembly are intriguing tools for the construction of extended structures. By taking advantage of the coordination preferences of metal ions and multitopic organic ligands, a seemingly unlimited diversity of metal-organic coordination networks (MOCN) can be prepared that offer a wide range of structural and physical properties. We will design extended structures (molecular wires, 3-D coordination polymers) as well as discrete molecules of nanometer dimensions that incorporate redox-active building blocks. Such materials may have applications as catalysts, conductive, luminescent, and porous materials (e.g., separation, size-selective adsorption of small molecules, gas storage, molecular recognition, sensing). Along with synthetic and structural interests, our key objectives involve molecules and cavities of defined sizes and shapes, the accessibility of open coordination sites, and the electronic properties of metal centers.

Methods. The research projects in our group offer training in synthetic chemistry (organic ligands, inorganic syntheses), spectroscopic methods of analysis (optical absorption, multinuclear NMR, IR, Raman, and X-ray absorption spectroscopy), electrochemical methods, and X-ray crystallography.