Katia Bernardo-Gusmão

Biphasic oligomerization of ethylene with nickel–1,2-diiminophosphorane complexes immobilized in 1-n-butyl-3-methylimidazolium organochloroaluminate

Abstract Nickel(II)–diiminophosphorane complexes combined with alkylaluminum co-catalysts are active for the oligomerization of ethylene under biphasic reaction conditions. As observed in homogeneous phase, the selectivity (dimers vs higher oligomers) is related to the nature of the diiminophosphorane ligands. In 1- n -butyl-3-methylimidazolium organoaluminate ionic liquids, an enhancement of the catalytic activity and convergence of the selectivity are observed upon repeating cycles. These data suggest that organoaluminate anions replace the diiminophosphorane ligands in the coordination sphere of the active nickel species.

NiCl2(1,2-Diiminophosphorane) complexes: a new family of readily accessible and tuneable catalysts for oligomerisation of ethylene

1,2-Diiminophosphoranes 1–4 featuring either ethane, benzene, cyclohexane or 1,2-diphenylethane carbon backbones act as tightly bonded 1,4-chelating ligands towards NiCl2, affording the corresponding paramagnetic complexes 5–8 in high yield. X-Ray diffraction studies performed on compounds 5 and 6 revealed that the conformation of the five-membered metallacycle depends on the rigidity of the carbon backbone. For both complexes, the coordination sphere of the Ni atom is a distorted tetrahedron with bond lengths and angles around nickel similar to those observed for related Ni(II)(α-diimine) complexes. Complexes 5–8 are active for ethylene oligomerisation under mild reaction conditions (0°C, 1.1 bar) upon activation by alkylaluminum derivatives (Et2AlCl or MAO). The nature of the carbon backbone of the 1,2-diiminophosphorane ligands has a profound impact on the selectivity of the catalytic systems. The selectivity for trimers and higher oligomers varies from 10% (pre-catalyst 8) to 81% (pre-catalyst 5). Effects of varying ethylene pressure, temperature and aluminium co-catalyst/nickel ratios with pre-catalyst 6 are reported. Tailoring the reaction parameters has a modest effect on the oligomer distribution but allows quite high catalytic activities to be achieved with turnover frequencies up to 135×103 h−1.

An Introduction to Zeolite Synthesis Using Imidazolium-Based Cations as Organic Structure-Directing Agents

Zeolite synthesis is a wide area of study with increasing popularity. Several general reviews have already been published, but they did not summarize the study of imidazolium species in zeolite synthesis. Imidazolium derivatives are promising compounds in the search for new zeolites and can be used to help understand the structure-directing role. Nearly 50 different imidazolium cations have already been used, resulting in a variety of zeolitic types, but there are still many derivatives to be studied. In this context, the purpose of this short review is to help researchers starting in this area by summarizing the most important concepts related to imidazolium-based zeolite studies and by presenting a table of recent imidazolium derivatives that have been recently studied to facilitate filling in the knowledge gaps.

Ethylene polymerization with a nickel diimine catalyst covalently anchored on spherical ZSM-5

Late transition catalysts play an important role in the catalytic conversion of olefins into polymers with different microstructures. Homogeneous nickel-based catalysts are known for their outstanding activity and low metal cost. However, the homogeneous nature of the catalysts is a major disadvantage and does not fit current heterogeneous processes. Some advantages that justify the heterogenization of these catalysts include the ability to perform polymerization reactions using small amounts of solvent or no solvent, polymer growth control and decades of industrial improvements. In this study, we propose the use of a spherical ZSM-5 zeolite as a support for a nickel diimine catalyst, with the expectation that morphological replication of the support would be observed in an ethylene polymerization reaction. First, the zeolite was pre-treated with trimethylaluminium (TMA), followed by the addition of the catalyst (dibromo-bis(4-amino-2,3,5,6-tetramethylphenylimino)-acenaphtenenickel[II]). The covalently anchored catalyst was used under different conditions and compared with the homogeneous catalyst. During polymerization with TMA at 60 °C, the productivity reached nearly 1000 kg PE mol(Ni)−1 h−1 for both catalysts. When the experiments were performed at 10 °C, the productivity increased to 4408 and to 3764 kg PE mol(Ni)−1 h−1 for the homogeneous and heterogenized catalysts, respectively. Methylaluminoxane (MAO) was also used and further improved the productivity to 14 000 kg PE mol(Ni)−1 h−1 for both systems. Morphological replication was observed, especially in the first stages of the polymerization process. The zeolite showed good influence on morphological control due to the morphological replication and we achieved a highly active heterogenized catalyst compared to the homogeneous analogue.

Polymerization of Ethylene with Zirconocene Heterogenized on Spherical ZSM-5

Homogeneous polymerization catalysts require large amounts of solvent and cannot control the polymer morphology. In order to solve this issue, a narrow-shaped spherical ZSM-5 zeolite was used in ethylene polymerization as a support for zirconocene (Cp2ZrCl2). Several heterogeneous catalytic precursors were prepared and used in ethylene polymerization reactions, which showed yields (between 980-8019 kg PE mol-1 h-1) and were efficient at promoting morphological replication of the support. So, a well-established protocol for slurry polymerization reaction was found, yielding well-defined polymer particles in an advantageous polymerization process.

SBA-15 as a Support for Nickel-Based Catalysts for Polymerization Reactions

Two mesoporous SBA-15 materials with different morphologies (spherical and fiber-shaped) were synthesized and evaluated as supports for nickel-based catalysts for polymerization reactions. The supports were pretreated with trimethylaluminum (TMA), and the catalyst dibromo-bis(4-amino-2,3,5,6-tetramethylimino)acenaphthene nickel(II) was attached to the supports and activated with TMA or MAO (methylaluminoxane). Characterization showed that the insertion of cetyltrimethylammonium bromide (CTABr) as a cosurfactant led to spherical SBA-15 with a decrease in particle and pore sizes to 4.8 nm compared to 6.5 nm in traditional fiber-shaped SBA-15. The spherical SBA-15 showed thicker walls than the fiber-shaped SBA-15, attributed to the increase in functional groups of the cosurfactant. The different spherical and fiber-shaped morphologies did not show any significant difference in the productivity of polyethylene. The catalyst supported on spherical SBA-15 materials showed 58% productivity compared to its homogeneous analogue using TMA as a cocatalyst.