| | Assistant Professor
Ph D., Northwestern University
Inorganic Chemistry Information
My research interests fall within inorganic chemistry, broadly defined to include classical coordination chemistry as well as organometallic chemistry, and encompass synthetic, structural, and mechanistic perspectives. We are particularly inspired by the various biological metalloenzymes and cofactors that carry out such difficult reactions as carbonylation, hydrocarbon bond substitution, and dinitrogen hydrogenation, often with high selectivities and under ambient conditions. Our interests are further driven by a wealth of recent structural data obtained for enzymatic metal centers. Such biochemistry is often compared to analogous industrial reactions that rely on harsh and frequently inefficient conditions; many such processes will eventually require increased economy or alternative feedstocks to remain viable. For this reason, functional modeling that explores for new and potentially useful stoichiometric and catalytic reactivities retains fundamental importance. An initial target for a functional modeling investigation will be the unique bioorganometallic chemistry of Carbon Monoxide Dehydrogenase/Acetyl Coenzyme-A Synthase (CODH/ACS). This bacterial enzyme features distinct, structurally characterized nickel-containing active sites that enable terminal acetate formation from carbon dioxide. The mechanistic details of the actual acetogenic enzymology remain to be fully elucidated, but clear parallels have been drawn between the title activities, which occur at disparate sites, and both an industrial water-gas shift reaction and the well-known Monsanto Acetic Acid process, respectively. While the latter is a paradigmatic industrial application of homogeneous catalysis, the reaction nonetheless requires a precious metal catalyst, a corrosive promoter, high reaction temperatures, and significant carbon monoxide pressures to attain analogous carbonylation of methyl alcohol. Our efforts will focus on design of biomimetic nickel complexes that allow for mechanistic study of plausible component reaction steps of the ACS activity, such as migratory CO insertion, thiol ligation, and reductive elimination of thioester equivalents. The biological reaction also requires formal enzyme-mediated transfer of a methyl cation from cobalamin to nickel, and modeling of this specific step with tethered bimetallic cobalt/nickel conjugates is also of interest. Transition metal complexes can adopt a wide range of oxidation states and a seemingly unlimited variety of π-bonding motifs, such that the opportunity to prepare new complexes with unique chemical properties is plainly evident. Accordingly, a second area of interest is the preparation of organometallic coordination polymers in which the metal centers are bridged by acetylide (-C≡C-) linkers. Prototypical examples were reported in 1975 by Hagihara and coworkers (Osaka), who found that trans-diacetylide complexes of platinum(II) could be oxidatively coupled to form linear polymers incorporating up to 200 metal centers. The polymer chains necessarily form rigid rods that must approach 160 nanometers in length. Moreover, concentrated solutions adopt a liquid crystalline phase in which the polymer rods are fully aligned. These properties would seem to be ideal for a nanoscale “molecular wiring,” but the closed-shell nature of the incorporated metal ions precludes facile electron delocalization, and the materials exhibit optical bandgaps in excess of 3.0 eV, consistent with weak semiconducting behavior. Theoretical studies have predicted that analogous polymers containing open-shell metal ions, for example octahedral d2 and d4 configurations, will exhibit high intrinsic conductivities, but such materials remain unknown. We propose to direct an exploratory synthetic effort towards the preparation of such species.
Selected Publications Michael P. Jensen, Antoni Mairata i Payeras, Miquel Costas, József Kaizer, Audria Stubna, Eckard Münck, and Lawrence Que, Jr. "Kinetic Analysis of the Conversion of Nonheme Alkylperoxoiron(III) Species to Iron(IV) Complexes." Inorg. Chem., 2007, ASAP.
Eric J. Klinker, Timothy A. Jackson, Michael P. Jensen, Audria Stubna, Gergely Juhasz, Emile L. Bominaar, Eckard Münck, and Lawrence Que, Jr. "A Tosylimido Analog of a Nonheme Oxoiron(IV) Complex. Angew. Chem. Int. Ed., 2006, 45, 7394-7397.
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.
Michael P. Jensen, Emily L. Que, Xiaopeng Shan, Elena Rybak-Akimova and Lawrene Que, Jr. "Spectroscopic and Kinetic Studies of the Reaction of [CuI(6-PhTPA)]+ with O2." Dalton Transactions 2006, 3523-3527. Michael P. Jensen, Miquel Costas, Raymond Y. N. Ho, József Kaizer, Antoni Mairata i Payeras, Eckard Münck, Lawrence Que, Jr., Jan-Uwe Rohde, and Audria Stubna. "High-Valent Nonheme Iron. Two Distinct Iron(IV) Intermediates Derived from a Common Iron(II) Precursor." J. Am. Chem. Soc. 2005, 127, 10512-10525. Michael P. Jensen, Mark P. Mehn, and Lawrence Que, Jr. "Intramolecular Aromatic Amination Through Iron-mediated Nitrene Transfer." Angew. Chem. Int. Ed. 2003, 42, 4357-4360. Michael P. Jensen, Steven J. Lange, Mark P. Mehn, Emily L. Que, and Lawrence Que, Jr. "Biomimetic Aryl Hydroxylation Derived from Alkyl Hydroperoxide at a Nonheme Iron Center. Evidence for an Fe(IV)=O oxidant." J. Am. Chem. Soc. 2003, 125, 2113-2128. Michael P. Jensen, Douglas D. Wick, Stefan Reinartz, Peter S. White, Joseph L. Templeton, and Karen I. Goldberg. "Reductive Elimination/Oxidative Addition of Carbon-Hydrogen Bonds at Pt(IV)/Pt(II) Centers: Mechanistic Studies of the Solution Thermolyses of TpMe2Pt(CH3)2H." J. Am. Chem. Soc. 2003, 125, 8614-8624 Michael P. Jensen and Dennis P. Riley. "Peroxynitrite Decomposition Activity of Iron Porphyrin Complexes." Inorg. Chem. 2002, 41, 4788-4797.
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