Rauchfuss Group

Supramolecular Organometallic Chemistry in Separations and Catalysis

A project supported by the U. S. Department of Energy
(DOE DEFG02-90ER14146)

Principal Investigator: Thomas B. Rauchfuss

Coworkers:
Julie Boyer, B.S. University of Buffalo
Zachariah Heiden, B.S. University of Wisconsin
Swarna Kokatam, Ph.D. MPI für Bioanorganische Chemie
Mark Ringenberg, B.S. University of Pittsburgh
Aaron Royer, B.S. Indiana University

Recent alumni:
Jonathan G. Breitzer, Assistant Professor, Fayetteville College
Stephen M. Contakes, Assistant Professor, Westmont College
Amanda L. Eckermann Postdoc, Northwestern Univ.
Kevin Klausmeyer, Associate Professor Baylor University
Matt Kuhlman, Research Scientist, GE
Robert F. Pafford, Research Scientist, Rohm and Haas
Andrew C. Moreland, Research Scientist, Albemarle Catalysts
Maya Ramesh, X-ray Crystallography Lab, University of Illinois, UC
Daniel E. Schwarz, Postdoc, LANL
Markus Wunder, Research Scientist, Ohmx

Overview.
In this project we apply organometallic chemistry to basic issues related to energy processing, catalysis, and environmental remediation. The era of examining simple unfunctionalized ligands attached to one or a few metals is mature, and growth is associated with the molecules of greater complexity and functionality, as embodied in the areas of supramolecular chemistry and nanoscience. Molecules are bigger than before and expectations for selectivity and green-ness are high. Synthesis continues to play a major role, but is increasingly guided by information on weaker forces and by in situ techniques that probe transformations on the fly.

• Container molecules. Our container project is premised, broadly speaking, on the expectation that geometrically rigid, kinetically robust container molecules will increasingly become part of our technological culture. Machines of the future will rely on these molecules for plumbing and packaging. In this project we are preparing large organometallic cage compounds based on CN-linked multimetallic arrays. Well defined, kinetically robust, container molecules are difficult to prepare. Synthetic chemists are expected to elucidate design rules that will guide this effort. And simply being large is not enough, the molecules must be smart (functional) and in our hands at least, soluble. We discovered a templated method to induce condensation of CpCo(CN)₃^- and Cp*Ru(MeCN)₃⁺ to quantitatively produce the organometallic box [CpCo(CN)₃]₄[Cp*Ru]₄:
  
  
  This species display a pronounced affinity for Cs⁺ even in the presence of substantial excess of K⁺. ¹³⁷Cs⁺ in the presence of excess K⁺ presents an environmental problem associated with clean-up of nuclear wastes.


• Non-innocent Ligands in Catalysis. Non-innocent describes ligands that undergo redox at potentials similar to those of the attached metals. Thus, both the metal and the ligand can undergo redox. Nature uses such ligands extensively, for example in O₂ activation. Coordination chemists have been interested in them for decades, but surprisingly little work has been aimed at their use in synthetic catalysts, mainly because such ligands are rarely studied by coordination chemists. We have developed a family of half-sandwich complexes of non-innocent ligands for use in activation of hydrogen and related small molecules. The ligands are related to the hybrid phenylenediamines.


• Second Coordination Sphere Control with 2-Pyridones. We are examining the role of 2-hydroxypyridines (2-pyridones) in catalysis and coordination chemistry. Pyridines are well known as ligands, and the presence of the 2-hydroxy group presents an easy and versatile method for influencing the second coordination sphere of the associated complex. We are also studying the species 2-hydroxypyridine-6-acetic acid, an analogue of cofactor GP which occurs in the methanogenesis pathway. A family of coordination complexes have been prepared and the main focus is on structural models for biological H₂-transfer catalysts.


• Metal-Amine-Hydrides as Prototype Catalysts for Fuel Cells. The very simple reaction O₂ + H₂ is both exothermic and slow in the absence of catalysts. We suggest that by elucidating pathways to accelerating this reaction, one might learn information that would inspire the design of new catalysts for fuel cells. Our main discovery is that Cp*Ir(NR₂)(NH₂R)H are excellent catalysts for this reaction. A key aspect of the catalysis is the participation of the N-H center in the hydrogenation of the dioxygen (See Figure).
  
  Figure: Optical spectra for the hydrogenation of O₂ by Cp*IrH(TsDPEN).
  
  
  

Representative Recent Publications

"Supramolecular Architectures Based on Organometallic Half-sandwich Complexes",T. B. Rauchfuss, K. Severin, in Molecular Nanostructures J. Atwood, J. Steed, eds. (2007 in press).

"Homogeneous Catalytic Hydrogenation of Dioxygen: a Step Toward an Organometallic Fuel Cell?" Z. M. Heiden, T. B. Rauchfuss, (submitted 5/2007).

"Cyanometallate Cages with Exchangeable Terminal Ligands", J. L. Boyer, H. Yao, M. L. Kuhlman, T. B. Rauchfuss, S. R. Wilson, Eur. J. Inorg. Chem. (invited paper for 10th anniversary issue).

"Evolution of Organo-cyanometallate Cages: Supramolecular Architectures and New Cs⁺-specific Receptors", J.L. Boyer, M.L. Kuhlman and T.B. Rauchfuss, Accounts of Chemical Research, 2007, 40, 233-242.

"Redox-Switched Complexation/Decomplexation of K⁺ and Cs⁺ by Molecular Cyanometalate Boxes", J. L. Boyer, M. Ramesh, H. Yao, T. B. Rauchfuss, S. R. Wilson, J. Am. Chem. Soc. 2007, 129, 1931-1936.

"Proton-induced Lewis Acidity of Unsaturated Iridium Amides", Z. M. Heiden and T. B. Rauchfuss, J. Am. Chem. Soc. 2006, 128, 13048-13049.

"Competing H-H, S-S, and M-M Bond Formation in [Ru₄S₃(arene)₄]z Clusters" M. L. Kuhlman, T. B. Rauchfuss, Angew. Chem. Int. Ed. 2004, 43, 6742-6745.

"Synthesis and Characterization of the Hexagonal Prismatic Cage {THF[PhB(CN)₃]₆[Cp*Rh]₆}⁶⁺", M. L. Kuhlman, H. Yao, T. B. Rauchfuss, Chem. Commun. 2004, 1370-1.

"Hybrid Cluster-Cages Formed via Cyanometallate Condensation: CsCo₄Ru₆S₂(CN)₁₂, Co₄Ru₉S₆(CN)₉, and Rh₄Ru₉S₆(CN)₉ Frameworks", M. L. Kuhlman, T. B. Rauchfuss, Inorg. Chem. 2004, 43, 430-435.

"Research on Soluble Metal Sulfides: From Polysulfido Complexes to Functional Models for the Hydrogenases" T. B. Rauchfuss, Inorg. Chem. 2004, 43, 14-26.