Our main research interests are directed towards the design of novel organometallic complexes for use as practical catalysts in olefin oligomerization and polymerization processes. The Group employs a ligand-oriented design approach to target and stabilize single-site catalysts. Objectives of this research include the synthesis, characterization (X-ray diffraction, NMR, El, Anal., etc.) and reactivity studies of the target molecules.

Group 4-5 catalysts for olefin polymerization

In the recent years, we have been interested in exploring the chemistry of Group 4 complexes based on sterically hindered tris(pyrazolyl)borate ligands (Tp´= generic substituted tris(pyrazolyl)borate) with the goal of developing novel olefin polymerization catalysts. Tp´ ligands are formally analogous to cyclopentadienyl (Cp) ligands in that both are six-electron-donor uninegative ligands. However, Tp´ ligands are 3-fold-symmetric -N donors and tend to form fac-octahedral complexes, while Cp ligands are typically 5-fold symmetric -C donors and tend to form tetrahedral complexes. Our studies in this field have demonstrated that sterically hindered Tp´TiCl3[ , ] and Tp´VCl2(NR) pre-catalysts [Tp´= HB(3-mesityl-pyrazolyl)3 (TpMs)-; HB(3-mesitylpyrazolyl) 2(5-mesityl-pyrazolyl) (TpMs*)-] (Figure 1) show high catalytic activity for polymerization of ethylene in the presence of methylaluminoxane.



Figure 1. Titanium and vanadium catalysts containing sterically hindered hydrotris(pyrazolyl)borate Ligands.

The immobilization of these soluble catalysts on inorganic supports such as MAO-modified silicas,[ ] SiO2, SiO2–Al2O3, MgCl2, MCM-41 and MgO[ ] affords highly active heterogeneous catalysts for ethylene polymerization in presence of common alkylaluminum co-catalyst (TEA, DEAC, TMA, and TiBA). Futhermore, we have demonstrated that the in situ immobilization of these Ti and V catalysts on MAO-modified silica are able to produce high-density polyethylenes with different properties depending on the cocatalyst nature, [Al]/[M] molar ratio, and the temperature of polymerization.[ , ]


Chromium and nickel catalysts based on tridentate ligands for ethylene oligomeZ rization

The pursuit of ethylene oligomerization catalysts capable of selectively producing -olefins has been a major focus of research in recent decades, due to their importance in a variety of industrial processes. Particularly, we have been much interested in the use of tridentate bis(pyrazolyl) NZN-type ligands (Z = N, O, S) for metal-catalyzed oligomerization processes. We have thus previously communicated new classes of NiII[ , ] and CrIII [ ]complexes based on these tridentate Z-bridged bis(pyrazolyl) ligands (Figure 2), which act as highly selective and highly active pre-catalysts for ethylene oligomerization in the presence of methylaluminoxane (MAO) as co activator. More recently, we have introduced a new set of NiII complexes based on NZN ligands that form stable 5-membered chelate rings which, in association with an alkylaluminum (MAO or AlEt2Cl), show high activity in ethylene oligomerization.



Figure 2. Chromium and nickel catalysts based on tridentate pyrazolyl-ligands for ethylene oligomerization.

Nanocomposites by in situ polymerization process

In recent years, polymer-clay nanocomposites have attracted much academic and industrial interest because of the anticipated improvements in mechanical properties, stiffness, thermal stability, chemical resistance, high barrier properties, flame retardancy, etc. when the aluminosilicate platelets of clays like montmorillonite are well exfoliated into polymers. Several methods have been adopted to prepare polymer-clay nanocomposites, such as self-assembly of exfoliated inorganic layers with polymers, template synthesis of layered crystals in the polymer solution, melting intercalation, and direct ion exchange of polyelectrolyte with hosts. More recently, special attention has been devoted to in situ intercalative polymerization methodology which is frequently also referred to as ‘‘polymerization filling’’. In this process, the monomer together with the polymerization initiator or catalyst is intercalated within the silicate layers and the polymerization is initiated either thermally or chemically. Moreover, polymerization filling process can produce nanocomposites with much higher nanofiller content. Our fighting in this area involves the intercalation of TpMs*TiCl3 into the organophilically modified montmorillonite clay (Cloisite 30B) (Figure 3), and its application in the production of UHMWPE-layered silicate nanocomposites.[ ] Both XRD and TEM results confirmed the uniform distribution of silicate layers of MMT in the whole PE matrix and the production of exfoliated PE-MMT nanocomposites. Some mechanical properties such as flexural modulus and storage modulus of PE-MMT nanocomposites showed some improvements when compared with those ones displayed by the neat PE.



Figure 3. Intercalation of TpMs*TiCl3 into Cloisite® 30B and TEM image for a PE-C30BH nanocomposite containing 5 wt % of organo-modified montmorillonite.

Selected References

1. (a) CASAGRANDE JUNIOR, O. L., JORDAN, R. F., MURTUZA, S. Ethylene Polymerization Behavior of Tris(pyrazolyl)borate Titanium (IV) Complexes. Organometallics. , v.21, p.1747 - 1753, 2002. doi:

2. CASAGRANDE JUNIOR, O. L., GIL, Marcelo P Titanium and Zirconium Complexes Containing Sterically Hindered Hydrotris(pyrazolyl)borate Ligands: Synthesis, Structural Characterization, and Ethylene Polymerization Studies. Journal of Organometallic Chemistry. , v.689, p.286 - 292, 2004.

3. GIL, M. P., SANTOS, João Henrique Zimnoch dos, CASAGRANDE JUNIOR, O. L. Polymerization of ethylene by the tris(pyrazolyl)borate titanium (IV) compound immobilized on MAO-modified silicas. Journal of Chemical Catalysis. A, Chemical. , v.209, p.163 - 169, 2004.

4. CASAGRANDE JUNIOR, O. L., CASAGRANDE, Adriana Curi Aiub, SANTOS, J. H. Z. dos, KUHN, Maria Cristina, TAVARES, Tatiana Tris(pyrazolyl)borate imido vanadium (V) immobilized on inorganic supports and its use in ethylene polymerization. Journal of Chemical Catalysis. A, Chemical. , v.212, p.267 - 275, 2004.

5. CASAGRANDE JUNIOR, O. L., GIL, Marcelo P Ethylene polymerization using tris(pyrazolyl)borate titanium (IV) catalyst supported in situ on MAO-modified silica. Applied Catalysis. A, General. , v.332, p.110 - 114, 2007.

7. CASAGRANDE JUNIOR, O. L., CASAGRANDE, Adriana Curi Aiub, GAMBA, Douglas, SANTOS, João Henrique Zimnoch dos, ANJOS, Patrícia S dos Ethylene polymerization using tris(pyrazolyl)borate vanadium (V) catalysts in situ supported on MAO-modified silica. Journal of Chemical Catalysis. A, Chemical. , v.255, p.19 - 24, 2006.

8. (a) CASAGRANDE JUNIOR, O. L., CARPENTIER, Jean Francois, KUNH, Maria Cristina Araujo, BOFF, Andressa, HORNER, Manfredo, AJELLAL, Noureddine Nickel Complexes based on Tridentate Pyrazolyl- Ligands for Highly Efficient Dimerization of Ethylene to 1-Butene. Organometallics. , v.25, p.1213 - 1216, 2006.

9. CASAGRANDE JUNIOR, O. L., LOSCH, Lucilene, CARPENTIER, Jean Francois, Campedelli, R. Roberta, KUNH, Maria Cristina Araujo Highly Selective Nickel Catalysts for Ethylene Oligomerization Based on Tridentate Pyrazolyl Ligands. Journal of Chemical Catalysis. A, Chemical. , v.288, p.58 - 62, 2008.

10. CASAGRANDE JUNIOR, O. L., KUHN, M. C. A., SANTOS, A. H., CARPENTIER, Jean François, THOMAS, Christophe, RABELLO, Carlos René Klotz, JUNGES, Fernando Chromium Catalysts Based on Tridentate Pyrazolyl Ligands for Ethylene Oligomerization. Organometallics. , v.26, p.4010 - 4014, 2007.

11. JUNGES, Fernando, BEAUVALET, Mariana Silva, LEAL, B., MOTA, F., CASAGRANDE, Adriana Curi Aiub, MAULER, Raquel Santos, CASAGRANDE JUNIOR, O. L. UHMWPE-Layered Silicate Nanocomposites by In Situ Polymerization with Tris(pyrazolyl)borate Titanium /Clay Catalyst. Journal of the Brazilian Chemical Society., v.20, p.472 - 477, 2009.