Assistant Professor
Ph D., Northwestern University
Inorganic Chemistry

Our research interests fall within inorganic chemistry, broadly defined to include classical coordination chemistry as well as organometallic chemistry, and to encompass synthetic, structural, and mechanistic perspectives. Our efforts are particularly inspired by nickel-dependent metalloenzymes utilized by anaerobic bacteria to carry out environmentally significant reactions including hydrogen activation, CO2 reduction, methane formation and superoxide dismutation. In some cases, this biochemistry is directly analogous to industrial reactions that operate less efficiently under harsh conditions at high temperatures and pressures. One such example is the bifunctional Carbon Monoxide Dehydrogenase/Acetyl Coenzyme-A Synthase (CODH/ACS) enzyme that couples a water/gas shift reaction (CO2 + H2 ↔ CO +H2) to a carbonylation reaction (CO + MeX + RSH → MeC(O)SR + HX) clearly resembling the archetypical Monsanto Acetic Acid synthesis. Other enzymology suggests accessible new technology, such as H2 activation and redox processes involving O2 that might be coupled to make an inexpensive fuel cell utilizing a cheap base metal in place of platinum. Furthermore, many of the pertinent active sites feature low-coordinate, sulfur-containing ligand fields that enable access to high-spin nickel(II) and high-valent nickel(III) intermediates in unusual geometries. While much of the known nickel enzymology appears to be an evolutionary artifact of an ancient reducing biosphere, a unique opportunity is paradoxically suggested to pursue new coordination chemistry in modeling studies of fundamentally important reaction chemistry. For this reason, we are interested in preparing functional models that will enable us to explore novel active site dynamics and reactivity. 

Our strategy is exemplified by synthesis of hydrotris(pyrazolyl)borato complexes of nickel(II) with dithiocarbamate co-ligands as models for a nickel-dependent superoxide dismutase (vide infra). A key feature of the enzyme active site within a trianionic N3S2 ligand field is an axial His-1 donor that can reversibly bind to the metal, stabilizing a Ni(II)/Ni(III) couple essential to turnover (cf. D. P. Barondeau, et al. Biochemistry 2004, 43, 8038). Similar to the enzyme, our synthetic complexes can adopt either a low-spin square-planar or a high-spin square-pyramidal configuration of a biomimetic ligand field that also supports a reversible one-electron redox couple in a range suitable for SOD activity. A key mechanistic question now accessible to biomimetic studies is the role of axial base ligation in controlling the redox chemistry.

Swarup Chattopadhyay, Tapash Deb, Jeffrey L. Petersen, Victor G. Young, Jr. and Michael P. Jensen.  “Steric Titration of Arylthiolate Coordination Modes at Pseudotetrahedral Nickel(II) Centers.”  Inorg. Chem.  2009, in press. 

Huaibo Ma, Guangbin Wang, Gordon T. Yee, Jeffrey L. Petersen, and Michael P. Jensen.  “Scorpionate-supported models of nickel-dependent superoxide dismutase” (invited contribution to the Swiatoslaw Trofimenko memorial issue).  Inorg. Chim. Acta  2009, 362, 4563-4569.

Huaibo Ma, Swarup Chattopadhyay, Jeffrey L. Petersen, and Michael P. Jensen.  “Harnessing Scorpionate Ligand Equilibria for Modeling Reduced Nickel Superoxide Dismutase Intermediates.”  Inorg. Chem.  2008, 47, 7966-7968.

Swarup Chattopadhyay, Tapash Deb, Huaibo Ma, Jeffrey L. Petersen, Victor G. Young, Jr.  and Michael P. Jensen.  “Arylthiolate Coordination and Reactivity at Pseudotetrahedral Nickel(II) Centers:  Modulation by Noncovalent Interactions.”  Inorg. Chem.  2008, 47, 3384-3392

Shadrick I. M. Paris, Jeffrey L. Petersen, Evamarie Hey-Hawkins, and Michael P. Jensen.  “Spectroscopic Characterization of Primary and Secondary Phosphine Ligation on Ruthenium(II) Complexes.”  Inorg. Chem.  2006, 45, 5561-5567.