Dr. Thomas Weyhermüller - Chemical Synthesis, X-ray structure analysis

Dr. Thomas Weyhermüller
Leiter der Gruppe Chemical Synthesis, X-ray structure analysis
Abteilung Anorganische Spektroskopie

Vita

Diplom (Chemie)Ruhr-Universität Bochum (1989)
Ph.D., wiss. MA
Ruhr-Universität Bochum (1990-1994)
Dr. rer. nat.Ruhr-Universität Bochum (1994)
Gruppenleiter MPI für Bioanorganische Chemie; heute: MPI CEC (since 1995)

Publikationen

Selected Publications

  • R. Bjornsson, M.U. Delgado-Jaime, F.A. Lima, D. Sippel, J. Schlesier, T. Weyhermüller, O. Einsle, F. Neese, S. DeBeer: Mo L-Edge Spectra of MoFe Nitrogenase.
    Z. Anorg. Allg. Chem. 2015, 65-71
  • K. Weber, T. Weyhermüller, E. Bill, Ö.F. Erdem, W. Lubitz: Design and Characterization of Phosphine Iron Hydrides: Towards Hydrogen Producing Catalysts.
    Inorg. Chem. 2015, 54, 6928-6937
  • L. Rapatskiy, W. Ames, M. Perez Navarro, A. Savitsky, J. Griese, T. Weyhermüller, H. Shafaat, M. Högbom, F. Neese, D. Pantazis, N. Cox: Characterization of Oxygen Bridged Manganese Model Complexes Using Multifrequency 17O-Hyperfine EPR Spectroscopies and Density Functional Theory. J. Phys. Chem. 2015, 119, 13904-1392
  • R. Bjornsson, F.A. Lima, T. Weyhermüller, P. Glatzel, T. Spatzal, O. Einsle, E. Bill, F. Neese, S. DeBeer: Identification of a spin-coupled Mo(III) in the Nitrogenase Iron-Molybdenum Cofactor
    Chem. Sci. 2014, 5, 3096-310
  • D. Maganas, M. Roemelt, T. Weyhermüller, R. Blume, M. Hävecker, A. Knop Gericke, S. DeBeer, R. Schlögl, F. Neese: L-Edge X-Ray Absorption Study of Mononuclear Vanadium Complexes and Spectral Predictions Using a Restricted Open Shell Configuration Interaction Ansatz. Phys. Chem. Chem. Phys. 2014, 16, 264-27
  • K. Weber, Ö.F. Erdem, E. Bill, T. Weyhermüller, W. Lubitz: Modeling the Active Site of [NiFe]-Hydrogenases and the [NiFeu] Subsite of the C-Cluster of Carbon Monoxide Dehydrogenases: Low-Spin Iron(II) Versus High Spin Iron(II). Inorg. Chem. 2014, 53, 6329-633
  • A. Tondreau, S.C. Stieber, C. Milsmann, E. Lobkovsky, T. Weyhermüller, S. Semproni,
    P. Chirik: Oxidation and Reduction of Bis(imino)pyridine Iron Dinitrogen Complexes: Evidence for Formation of a Chelate Trianion. Inorg. Chem. 2013, 52, 635-64
  • M. Wang, J. England, T. Weyhermüller, S.  Kokatam, C.J. Pollock, S. DeBeer, J. Shen, G.P.A. Yap, K.H. Theopolt. K. Wieghardt: New Complexes of Chromium(III) Containing Organic p-Radical Ligands: An Experimental and DFT Computational Study. Inorg. Chem. 2013, 52, 4472-44
  • M. Wang, T. Weyhermüller, J. England, K. Wieghardt: Molecular and Electronic Structures of Six-Coordinate “Low-Valent” [M(Mebpy)3]0 (M = Ti, V, Cr, Mo) and [M(tpy)2]0 (M = Ti, V, Cr), and Seven-Coordinate [MoF(Mebpy)3](PF6) and [MX(tpy)2](PF6) (M = Mo, X = Cl and M = W, X = F). Inorg. Chem. 2013, 52, DOI 10.1021/ic402037
  • K. Weber, T. Krämer, H. Shafaat, T. Weyhermüller, E. Bill, M. van Gastel, F. Neese,
    W. Lubitz: A functional [NiFe]-hydrogenase model compound that undergoes biologically relevant reversible thiolate protonation. J. Am. Chem. Soc. 2012, 134, 20745-2075
  • C.C. Scarborough, S. Sproules, T. Weyhermüller, K.M. Lancaster, S. DeBeer, K. Wieghardt: Experimental Fingerprints for Redox-Active Terpyridine in [Cr(tpy)2](PF6)n (n = 3 - 0), and the Remarkable Electronic Structure of [Cr(tpy)2]1-. Inorg. Chem. 2012, 51, 3718-373
  • T. Birk, K.S. Pedersen, C.A. Thuesen, T. Weyhermüller, M. Schau-Magnussen, S. Piligkos, H. Weihe, S. Mossin, M. Evangelisti, J. Bendix: Fluoride Bridges as Structure-Directing Motifs in 3d-4f Cluster Chemistry. Inorg. Chem. 2012, 51, 5435-544
  • C.C. Scarborough, S. Sproules, C.J. Doonan, K.S. Hagen, T. Weyhermüller, K. Wieghardt: Scrutinizing Low-Spin Cr(II) Complexes. Inorg. Chem. 2012, 51, 6969-698
  • J. England, C.C. Scarborough, T. Weyhermüller, S. Sproules, K. Wieghardt: Electronic Structures of the Electron Transfer Series: [M(bpy)3]n, [M(tpy)2]n, and [Fe(tbpy)3]n (M = Fe, Ru; n = 3+, 2+, 1+, 0, 1-). A Mössbauer Spectroscopic and Density Functional Theory Study. Eur. J. Inorg. Chem. 2012, 4605-462
  • M. Khusniyarov, E. Bill, T. Weyhermüller, E. Bothe, K. Wieghardt: Hidden Non-innocence: Theoretical and Experimental Evidence for Redox Activity of the b-Diketiminiate(1-) Ligand. Angew. Chemie Int. Ed. 2011, 50, 1652-1655
  • S. Russel, C. Milsmann, E. Lobkovsky, T. Weyhermüller, P. Chirik: Synthesis, Electronic Structure and Catalytic Activity of Reduced Bis(aldimino)pyridine Iron Compounds: Experimental Evidence for Ligand Participation. Inorg. Chem. 2011, 50, 3159-316
  • S. Sproules, P. Banerjee, T. Weyhermüller, Y. Yan, J.P. Donahue, K. Wieghardt: Monoanionic Molybdenum and Tungsten Tris(dithiolene) Complexes: A Multi-Frequency EPR Study. Inorg. Chem. 2011, 50, 7106-7122
  • C.C. Scarborough, S. Sproules, T. Weyhermüller, S. DeBeer, K. Wieghardt: Electronic and Molecular Structures of the Members of the Electron Transfer Series [Cr(tbpy)3]n (n = 3+, 2+, 1+, 0): An X-ray Absorption Spectroscopic and Density Functional Theoretical Study. Inorg. Chem. 2011, 50, 12446-12462

Full publicationslist

Researcher ID

Funktionen & Aufgaben

  • since 2000 head of the analytical und preparative GC/HPLC-group

Gruppenmitglieder

Postdocs

  • Natalia Levin Rojas
  • Dr. Sivathmeehan Yogendra

Labor

  • Fabian Otto
  • Martha Sojka

Chemical synthesis, X-ray structure analysis

Bringing Together Experimental Spectroscopy and Quantum Theory

Chemical activation of inert small molecules like carbon dioxide, methane, nitrogen and others is a key problem in energy research. In the future, energy from renewable sources will be used on a big scale to transform these abundant materials to chemicals for industry and agriculture. Metal catalysts are needed to make such transformations energetically and chemically efficient and selective. We strongly believe that a deep understanding of mechanistic functionality and electronic structure of catalytic systems vastly supports the process of developing better catalysts. It is our approach to combine spectroscopic methods (EPR, MCD, Mössbauer, Resonance Raman, X-Ray methods, etc.) with quantum theory to shine light on the chemical and electronic structure of catalytically active centers. The combination of experiment with theory allows to interpret even very complicated spectroscopic data and to extract the desired chemical information.

Research in my group focuses on the synthesis of metal complexes for spectroscopic investigations. Directed variation of structural and electronic parameters in a series of compounds allows to systematically studying their spectroscopic response. Our samples are typically analyzed by standard methods (elemental analysis, IR, UV/vis, NMR, XRD) before they are further investigated as mentioned above. Such compounds with known molecular structure provide a reliable basis to collect high quality spectroscopic data. In the following, two examples of recent projects are given.

Elucidating the electronic structure of a CO2-reducing catalyst

There are a number of homogenous catalysts known which can reduce carbon dioxide from industrial processes back to valuable chemicals like carbon monoxide, formic acid or formaldehyde. Direct hydrogenation with heterogeneous catalysts can even produce methanol from CO2.  One of the most promising methods to reduce CO2  to useful chemical building blocks is the electrochemical reduction employing an electrocatalyst. Unfortunately, the first reduction step forming the anion radical CO2•−  is at very negative potential and is associated with a huge over potential. Proton coupled reduction is much more favorable in this respect as shown in equation 1.1

eqn. 1 CO2 + e → CO2•−   E°′ = -1.90 V
 
CO2 + 2H+ 2e-→ CO + H2O   E°′ = -0.53 V
CO2 + 2H+ 2e-→ HCO2H   E°′ = -0.61 V
CO2 + 4H+ 4e-→ HCHO + H2O   E°′ = -0.48 V

 

Iron porphyrins have been investigated as potential electrocatalysts for quite some time now. In their super-reduced [(TPP)Fe]2– form - formally a "Fe(0)" state - they are known to act as potent electrocatalysts for CO2 reduction (Fig. 1). The groups of Costentin and Saveant recently added internal proton donor functionalities making the catalyst even more effective.2 There is, however, a lot of controversy on the exact nature of the electronic ground states of [(TPP)Fe]1– and [(TPP)Fe]2–, since the reductions can be either metal or ligand centered. We have therefore started a project to elucidate the electronic structure of these species since we feel that it is crucial to understand the catalytic mechanism to design new and more efficient catalysts.

Preparation of [(TPP)Fe]0/1-/2- species was done by stepwise reduction of [(TPP)Fe IIICl] (1) using the published procedure by Scheidt et al.3 Isolated complexes [(TPP)Fe(THF)2]0 (2) (S = 2), [(TPP)Fe]0 (3) (S = 1), and sodium salts of [(TPP)Fe]1- (4) (S = ½) and [(TPP)Fe]2- (5) (S = 0) were investigated using EPR, resonance Raman, Mössbauer and XAS spectroscopies. Structural parameters of all complexes and their spectroscopic properties were thoroughly calculated using DFT methods. Experimental results clearly evidence that the iron centers in 3, 4 and 5  are of the same, namely intermediate spin Fe(II) character (S=1), which is nicely demonstrated by XAS spectra shown in Figure 2. DFT studies of a hypothetical low spin d7 Fe(I) state for 4 and a low spin d8 Fe(0) state for show that the energy separations between low spin states and intermediate spin states are 188.5 and 47.9 kcal/mol higher in energy for low spin states, far beyond the error range of a DFT calculation. We found that spectroscopic results of the redox series [(TPP)Fe]0/1-/2– only fit with quantum chemical models if the reduction processes are ligand centered, not metal centered. Reduction equivalents are stored in the π*-orbital of the porphyrin ligand to form radical states which are antiferromagnetically coupled to the central intermediate spin iron(II) centers. The porphyrin ligand functions as an electron relay and donates the two electrons necessary to reduce CO2 to CO.

What is the oxidation state of molybdenum in the FeMoco-factor of nitrogenase?

Nitrogenase is a bacterial enzyme which catalyzes the conversion of nitrogen from air to ammonia, an essential source for the biosynthesis of nitrogen containing compounds like peptides or nucleobases. The activation of nitrogen is very challenging since it is probably the most inert small molecule one could think of. A lot has been learned about the chemistry and structure of nitrogenase but the actual exact electronic structure and the catalytic mechanism are still a myth.

One of the two metal containing co-factors in nitrogenase, namely FeMoco, has been identified to be the active site of the enzyme where nitrogen binds and ammonia is released. It is basically composed of seven iron-, a molybdenum-center, nine sulfides, and a light atom, probably interstitial carbide ion. A long debate is going on what the oxidation states of the metal centers are and what the role of molybdenum is. So far, most authors favored Mo(IV) as the oxidation level for the resting state but no final conclusion could be made. We felt challenged to contribute to the solution of this problem and started a project in which we prepared a number of molybdenum model complexes resembling structural features of the natural co-factor. Model complexes and the natural enzyme were investigated using a combined experimental and theoretical approach. High-energy resolution fluorescence detected XAS spectroscopy (HERFD-XAS) was used to analyze complexes and enzyme. This method is superior to normal XAS spectroscopy due to better energy resolution. A detailed computational study in which all meaningful combinations of oxidation states were calculated was performed and results were compared with experimental data. Our analysis shows that the molybdenum atom in FeMoco of Mo-dependent nitrogenase is best described as a Mo(III) coupled to the iron atoms in the cofactor (Figure 3). This is in sharp contrast to the previous description of the molybdenum as a closed-shell Mo(IV).

Crucial to this oxidation state assignment was to utilize HERFD-XAS as well as a direct comparison of the MoFe protein with synthetic [MoFe3S4]3+ model compounds. The electronic structure of the FeMo cofactor, however, is still not fully understood. Understanding the spin coupling between not only the irons but also molybdenum and irons will be an important topic of future studies. Similarly, understanding the effect of the interstitial carbon atom on the electronic structure remains an open question.

Structure Determination

In coordination chemistry structural determination is an absolute prerequisite to understanding properties of transition metal complexes. Furthermore, structure determination by single crystal X-ray diffraction is obligatory in coordination chemistry because our ability to obtain a target compound is limited and unexpected self-assembly phenomena sometimes prevail. X-ray structure analysis delivers highly precise information about the three-dimensional arrangement of atoms, thereby providing bond length and bond angles, which are of enormous importance in understanding chemical properties. Since it is our aim to correlate spectroscopic features and functional properties with structure, X-ray structure analysis is vital to this area of research.

Figure 4 shows a crystal structure from a recent publication in which we studied protonation properties of hydrogenase model complexes.5 Structures of both, unprotonated and protonated species could be determined and the protonation site could be clearly located.

 

References

[1] Benson, E. E.; Kubiak, C. P.; Sathrum, A. J.; Smieja, J. M. Chem. Soc. Rev. 2009, 38, 89-99.

[2] (a) Costentin, C.; Drouet, S.; Passard, G.; Robert, M.; Saveant, J. M. J. Am. Chem. Soc. 2013, 135, 9023-9031. (b) Costentin, C.; Passard, G.; Robert, M.; Saveant, J. M. J. Am. Chem. Soc. 2014, 136, 11821–11829.

[3] Mashiko, T.; Reed, C. A.; Haller, K. J.; Scheidt, W. R. Inorg. Chem. 1984, 23  3192 - 3196

[4] Bjornsson, R.; Lima, F.A.; Weyhermüller, T.; Glatzel, P.; Spatzal, T.; Einsle, O.; Bill, E.; Neese, F.; DeBeer, S.; Chem. Sci. 2014, 5, 3096-3103

[5] K. Weber, T. Krämer, H. Shafaat, T. Weyhermüller, E. Bill, M. van Gastel, F. Neese, W. Lubitz: A functional [NiFe]-hydrogenase model compound that undergoes biologically relevant reversible thiolate protonation. J. Am. Chem. Soc. 2012, 134, 20745-20755