4 years ago

The Role of Co-Activation and Ligand Functionalization in Neutral Methallyl Nickel(II) Catalysts for Ethylene Oligomerization and Polymerization

The Role of Co-Activation and Ligand Functionalization in Neutral Methallyl Nickel(II) Catalysts for Ethylene Oligomerization and Polymerization
René S. Rojas, Diana Yepes, Oleksandra S. Trofymchuk, Diego Cortés-Arriagada, Daniela E. Ortega, Alejandro Toro-Labbé, Soledad Gutiérrez-Oliva
A detailed quantum chemical study that analyzed the mechanism of ethylene oligomerization and polymerization by means of a family of four neutral methallyl NiII catalysts is presented. The role of the boron co-activators, BF3 and B(C6F5)3, and the position of ligand functionalization (ortho or para position of the N-arylcyano moiety of the catalysts) were investigated to explain the chain length of the obtained polymers. The chain initialization proceeded with higher activation barriers for the ortho-functionalized complexes (≈19 kcal mol−1) than the para-substituted isomers (17–18 kcal mol−1). Two main pathways were revealed for the chain propagation: The first pathway was favored when using the B(C6F5)3 co-activated catalyst, and it produced long-chain polymers. A second pathway led to the β-hydrogen complexes, which resulted in chain oligomerization; this pathway was preferred when the BF3 co-activated catalysts were used. Otherwise, the termination of longer chains occurred via a stable hydride intermediate, which was formed with an energy barrier of about 14 kcal mol−1 for the B(C6F5)3 co-activated catalysts. Significant new insights were made into the reaction mechanism, whereby neutral methallyl NiII catalysts act in oligomerization and polymerization processes. Specifically, the role of co-activation and ligand functionalization, which are key information for the further design of related catalysts, were revealed. The co-catalytic role of boron co-activators in neutral methallyl NiII catalysts is elucidated for its use in the polymerization and oligomerization of ethylene, which results in key information for the further design of catalysts (see figure).

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701571

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