The LMC has research under way in a number of areas involving the design, synthesis and characterization of new transition metal complexes, nanomaterials and ionic liquids (ILs, Figures 1) with special emphasis on their application in homogeneous, two-phase and supported catalysis. The catalytic reactions and process under investigation are based on the transformation of unsaturated substrates into molecular and macromolecular products. These reactions are mainly hydrogenation, oligomerization, polymerization, telomerization, carbonylation and oxidation of alkenes. Special attention is dedicated on the investigation of reaction mechanisms and kinetics. Brief summaries of several current Prof. Dr. Dupont’s and Ebeling’s Groups projects, along with examples of typical reactions under study, are given below.



Figure 1. Schematic 3-D representation of typical structural organization of imidazolium ILs.

Two-phase catalysis by organometallic catalysts precursors dissolved in ionic liquids

We have synthesized a new family of ionic liquids (molten salts) based on 1,3-dialkylimidazolium cation (Figure 2) that are air and water stable with a wide range of the liquid phase (down to –81°C depending on the nature of the anion and of the imidazolium-alkyl chain).1 These liquids are thermally and chemically stable under different conditions. These ILs are the immobilizing agents of choice for several catalytic reactions (hydrogenation, metathesis, carbonylation, arylation and telomerization of C=C bonds).2 Thus classical homogeneous catalytic reactions (including asymmetric)3 can now be run in typical two-phase systems where the products are simple removed from the reaction mixture by decanting and the recovered ionic catalyst solution can be reused several times without any significant changes on the catalytic activity or selectivity. In order to avoid catalyst leaching a series of ionophilic ligands4 (Figure 2) and their corresponding transition-metal complexes are designed, prepared and tested in various reactions. Further exploration of the chemistry of organometallic catalyst dissolved in these media and the investigation of the mechanism of their reactions are under way.



Figure 2. Examples of ILs and ionophilic ligands.

Transition-metal nanomaterials in ionic liquids

Imidazolium ILs posses pre-organized structures (Figure 1) that can adapt or are adaptable to many species, as they provide hydrophobic or hydrophilic regions and a high directional polarizability.5 This is one of the special qualities of imidazolium ILs that differentiates them from the classical ion aggregates of which ion pairs and ion triplets are widely recognized examples. This structural organization of ILs (Figure 1) can be used as “entropic drivers” for spontaneous, well-defined, and extended ordering of nanoscale structures. Indeed, the unique combination of adaptability towards other molecules and phases plus the strong hydrogen-bond-driven structure makes ionic liquids potential key tools in the preparation of a new generation of chemical nanostructures.6 We were amongst the first groups to recognize these properties and used imidazolium ionic liquids as a template, stabilizer, and solvent for the synthesis of a plethora of nanostructures, in particular transition-metal nanoparticles.7 The transition-metal nanoparticles (Figure 3) dispersed in these fluids are stable and active catalysts for some reactions in multiphase conditions. Inasmuch as most of the 1,3-dialkylimidazolium ionic liquids have extremely low vapor pressure and relatively high viscosity at room temperature, in situ TEM - which require high vacuum—can be performed with the MNPs dispersed in ILs.8 The catalytic properties (activity and selectivity) of these soluble metal nanoparticles indicate that they possess a pronounced surface like (multi-site) rather than single-site-like catalytic properties.9 In other cases the metal nanoparticles are not stable and tend to aggregate/agglomerate or serve as simple reservoirs for mononuclear catalytically active species.10 Further exploration of the chemistry of nanostructures dissolved in these media and the investigation of the their catalytic, magnetic and photo-physical properties are under way.



Figure 3. Examples of nanostructures prepared and characterized in imidazolium ionic liquids (in situ TEM micrographs): a) Co(0) nanocubes; b) spherical Ru(0) nanoparticles and c) worm-like Ir(0) nanoparticles.

Ionic liquids for the generation of clean energies.

The very unique properties of various 1,3-disubsituted imidazolium ILs such as noninflammable, high density, chemical and thermal stability, and very low vapor pressure is being used to design and prepare a series of new materials for clean energies. For example, it is well known cyclohexane reversibly yields six hydrogen atoms (7.1 mass %)and forms benzene, and stationary hydrogenation and dehydrogenations under steady-state conditions are managed in various chemical plants. However, the use of these compounds for on-board processes under variable conditions is likely to be problematic because cyclohexane derivatives and their dehydrogenated aromatics are volatile, inflammable, possess low density (meaning less hydrogen per volume ratio), and can decompose under the catalytic hydrogenation-dehydrogenation process. Fortunately, we access cyclohexane derivatives with very low vapor pressure, high density, and chemical and thermal stability, which are not inflammable by the simple introduction of an imidazolium cation to the cyclohexene moiety.11 These materials can add reversibly 6-12 hydrogen atoms (Figure 4) in the presence of classical Pd/C catalysts and can be used as alternative materials for on-board hydrogen-storage devices. These salts can hold up to 30 g L-1 of hydrogen at atmospheric pressure, which is twice that compressed hydrogen gas can attain at 350 atm.



Figure 4. Hydrogenation-dehydrogenation reactions of model hydrogen storage materials based on imidazolium salts.

ILs are also been used as immobilizing agents for classical acid/base catalysts, organometallic and biocatalysts for the generation of new process for the production of biodiesel.12-14

Selected References

1. Suarez, P. A. Z.; Dullius, J. E. L.; Einloft, S.; DeSouza, R. F.; Dupont, J., The use of new ionic liquids in two-phase catalytic hydrogenation reaction by rhodium complexes. Polyhedron 1996, 15 (7),1217-1219. doi:

2. Dupont, J.; de Souza, R. F.; Suarez, P. A. Z., Ionic liquid (molten salt) phase organometallic catalysis. Chemical Reviews 2002, 102 (10),3667-3691. doi: http://dx.doi.org/10.1021/cr010338r

3. Monteiro, A. L.; Zinn, F. K.; DeSouza, R. F.; Dupont, J., Asymmetric hydrogenation of 2-arylacrylic acids catalyzed by immobilized Ru-BINAP complex in 1-n-butyl-3-methylimidazolium tetrafluoroborate molten salt. Tetrahedron-Asymmetry 1997, 8 (2),177-179. doi:

4. Consorti, C. S.; Aydos, G. L. P.; Ebeling, G.; Dupont, J., Ionophilic phosphines: Versatile ligands for ionic liquid biphasic catalysis. Organic Letters 2008, 10 (2),237-240. doi: http://dx.doi.org/10.1021/ol702664a

5. Dupont, J., On the solid, liquid and solution structural organization of imidazolium ionic liquids. Journal of the Brazilian Chemical Society 2004, 15 (3),341-350. doi:

6. Migowski, P.; Dupont, J., Catalytic applications of metal nanoparticles in imidazolium ionic liquids. Chemistry-a European Journal 2007, 13 (1),32-39. doi: http://dx.doi.org/10.1002/chem.200601438

7. Dupont, J.; Fonseca, G. S.; Umpierre, A. P.; Fichtner, P. F. P.; Teixeira, S. R., Transition-metal nanoparticles in imidazolium ionic liquids: Recycable catalysts for biphasic hydrogenation reactions. Journal of the American Chemical Society 2002, 124 (16),4228-4229. doi: http://dx.doi.org/10.1021/ja025818u

8. Scheeren, C. W.; Machado, G.; Dupont, J.; Fichtner, P. F. P.; Texeira, S. R., Nanoscale Pt(0) particles prepared in imidazolium room temperature ionic liquids: Synthesis from an organometallic precursor, characterization, and catalytic properties in hydrogenation reactions. Inorganic Chemistry 2003, 42 (15),4738-4742. doi: http://dx.doi.org/10.1021/ic034453r

9. Scariot, M.; Silva, D. O.; Scholten, J. D.; Machado, G.; Teixeira, S. R.; Novak, M. A.; Ebeling, G.; Dupont, J., Cobalt Nanocubes in Ionic Liquids: Synthesis and Properties. Angewandte Chemie-International Edition 2008, 47 (47),9075-9078. doi: http://dx.doi.org/10.1002/anie.200804200

10. Cassol, C. C.; Umpierre, A. P.; Machado, G.; Wolke, S. I.; Dupont, J., The role of Pd nanoparticles in ionic liquid in the Heck reaction. Journal of the American Chemical Society 2005, 127 (10),3298-3299. doi: http://dx.doi.org/10.1021/ja0430043

11. Stracke, M. P.; Ebeling, G.; Cataluna, R.; Dupont, J., Hydrogen-storage materials based on imidazolium ionic liquids. Energy & Fuels 2007, 21 (3),1695-1698. doi: http://dx.doi.org/10.1021/ef060481t

12. Gamba, M.; Lapis, A. A. M.; Dupont, J., Supported ionic liquid enzymatic catalysis for the production of biodiesel. Advanced Synthesis & Catalysis 2008, 350 (1),160-164. doi: http://dx.doi.org/10.1002/adsc.200700303

13. Neto, B. A. D.; Alves, M. B.; Lapis, A. A. M.; Nachtigall, F. M.; Eberlin, M. N.; Dupont, J.; Suarez, P. A. Z., 1-n-Butyl-3-methylimidazolium tetrachloro-indate as a media for the synthesis of biodiesel from vegetable oils. Journal of Catalysis 2007, 249 (2),154-161. doi: http://dx.doi.org/10.1016/j.jcat.2007.04.015

14. Lapis, A. A. M.; deOliveira, L. F.; Neto, B. A. D.; Dupont, J., Ionic Liquid Supported Acid/Base-Catalyzed Production of Biodiesel. ChemSusChem 2008, 1,759-762. doi: http://dx.doi.org/10.1002/cssc.200800077