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

It is presented a detailed quantum chemical study analyzing the mechanism of ethylene oligomerization and polymerization by means of a family of four neutral methallyl NiII catalysts. The role of the boron co-activators [BF₃ or B(C₆F₅)₃] and ligand functionalization (in ortho or para position of the N-arylcyano moiety of the catalysts) was investigated to explain the chain length of the obtained polymers. The chain initialization proceeds with higher activation barriers for the ortho functionalized complexes (19 kcal mol¯¹) compared to the para isomers (17-18 kcal mol¯¹). Two main pathways were revealed for the chain propagation. The first pathway is preferred when using the B(C₆F₅)₃ co-activated catalyst, and it produce large chain polymers. A second pathway leads to the β-hydrogen complexes, which results in chain oligomerization; this pathway is preferred when the BF₃ co-activated catalysts are used. Otherwise, the termination of larger chains occurs via a stable hydride intermediate, which is formed with barriers of 14 kcal mol¯¹ for the B(C₆F₅)₃ co-activated catalysts. This work gives significant new insights into the mechanism whereby neutral methallyl NiII catalysts acts in oligomerization and polymerization processes, it clarifies the role of co-activation and ligand-functionalization, which are key information for further design of related catalysts.