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Forschungsarbeit

From potato starch to super absorber.
Carbenes as ancillary ligands in optimized catalyses

by Evangeline Tosh

Catalysts work by providing an alternative pathway to the formation of a given product. 
This alternate route results in a lower energy input, which can lower production costs. As such catalysts are not simply academic curiosities, but also of great industrial interest.  The goal of the Elite Doctorate Program NanoCat is the development and study of new nano-structured catalysts made from defined molecular (especially metal-organic) catalysts. The goal of my own research is the development and study of catalyst systems within a framework of green chemistry.  The twelve principles of green chemistry are listed below.

Principles of Green Chemistry
1. Prevention
2. Atom economy
3. Less hazardous chemical syntheses
4. Designing safer chemicals
5.  Safer solvents and auxiliaries
6.  Design for energy efficiency
7. Use of renewable feedstocks
8.  Reduce derivatives
9.  Catalysis
10. Design for degradation
11. Real-time analysis for pollution prevention
12. Inherently safer chemistry for accident prevention

In the Doctorate Program NanoCat, the group in the Professor Wolfgang A. Herrmann, is focused on the design and optimization of new complexes to be used as catalysts for a broad range of chemical transformations.  By introducing variance in the design motif of various well-bound elements (ligands) about the metal center the properties, stability and utility of resulting complexes (molecules containing metal elements) can be drastically altered.  My current focus is on the development of novel systems which contain carbocyclic carbenes as ligands.  Work done in cooperation with Christian Taubmann  has focused on the testing of these systems in C-C and C-N cross coupling.  Work recently published (Ref. 1) showed the advantages of the seven membered ring system in comparison to the three membered system. (Figure 1)

Advantages of the seven membered ring system in comparison to the three membered system[Bildunterschrift / Subline]: Figure 1: Yield vs. time plot for the coupling of p-bromo benzotrifluoride (1.0 mmol) with morpholine (1.2 mmol) at room temperature catalyzed by 0.5 equiv [LPdCl2]2 (I: __●__; II: --■--) in situ with 1.0 equiv PtBu3 (other conditions: 2.0 mol % Pd, 1.4 mmol NaOtBu, 8 ml toluene; GC yield with n-eicosane as the internal standard).

In addition to this work I have also been in cooperation with the group of Professor Fritz Kuehn. We have been evaluating the synthesis and utility of MTO (see Figure 2) within a framework of green chemistry.   Green chemistry is a philosophy of design where the focus is on minimizing the consumption of reagents and energy inputs, while optimizing the efficiency of the overall process.  The elucidation of the most efficient process is not only advantageous to the environment because the production of waste is minimized but also results in increased profits.  A green chemist not only thinks of how something can be done but also how something should be done to minimize the environmental impact of a given chemical reaction.  Rethinking current practices within a framework of green chemistry can lead to more sustainable chemical processes and industry.

Improved synthesis for methyltrioxo thenium (MTO)[Bildunterschrift / Subline]: Fig. 2: Improved synthesis for methyltrioxo thenium (MTO)

The broadest possible perspective is required when evaluating these systems and thus work in this area has resulted in collaborations within the TUM and beyond. By employing alternative solvents, reagents, energy sources and applying green chemistry metrics the optimal approach to product synthesis were established for various systems.(Figure 3)  Samples of this work can be found in recently published articles (see Ref. 2 and 3, figures 2 and 3).

From potato starch (renewable resource) to a super absorber (valuable product).[Bildunterschrift / Subline]: Figure 3: From renewable feedstock (potato starch) to super absorber

References:
1. C. Taubmann, E. Tosh, K. Öfele, E. Herdtweck, W. A. Herrmann, J. Organomet. Chem. 2008, 693, 2231-2236 (Carbocyclic Carbene Ligands in Palladium-Catalyzed C-N Coupling Reactions).

2. E. Tosh, J. K. M. Mitterpleininger, A. M. J. Rost, D. Veljanovski, W. A. Herrmann, F. E. Kühn, Green Chemistry 2007, 9(12), 1296-1298 (Methyltrioxorhenium revisited: improving the synthesis for a versatile catalyst).

3. W. A. Herrmann, A. M. J. Rost, E. Tosh, H. Riepl, F. E. Kühn, Green Chemistry
2008, 10 (4), 442-446 (Super absorbers from renewable feedstock by catalytic
oxidation).


Stationen
  • 2003-2006
  • M.Sc., University of Regina, Canada
  • seit 2006
  • Mitarbeiterin am Anorganisch-Chemischen Institut der TU München,
  • Mitglied im Internationalen Doktorandenkolleg NanoCat

  • Posterpräsentation
  • Tosh, Taubmann, and others (Herrmann): ACS National Meeting, New Orleans (USA), 03/2008 - Carbocyclic carbene complexes of palladium: Synthesis, structure, and catalysis.
  • Publikationen
  • Evangeline Tosh, Josef K. M. Mitterpleininger, Alexandra M. J. Rost, Draganco Veljanovski, Wolfgang A. Herrmann and Fritz E. Kühn, Methyltrioxorhenium revisited: improving the synthesis for a versatile catalyst, Green Chemistry., 2007, 9, 1296 – 1298.
  • Wolfgang A. Herrmann, Alexandra M. J. Rost, Evangeline Tosh, Herbert Riepl and Fritz E. Kühn, Super absorbers from renewable feedstock by catalytic oxidation, Green Chemistry, 2008, 10, 442-446.
  • Taubmann, Christiana; Tosh, Evangeline; Öfele, Karl; Herdtweck, Eberhardt; Herrmann, Wolfgang A., Carbocyclic carbene ligands in palladium-catalyzed C–N coupling reactions, Journal of Organometallic Chemistry, Volume Articles in Press, 2008.