Cationic η3-allylmetal complexes, 12. Oligomerization of styrene with cationic allylnickel compounds: Catalysts, products and the influence of phosphines

The complex [η3‐methylallyl(η4‐cycloocta‐1,5‐diene)nickel] hexafluorophosphate (2) was found to be an efficient catalyst for the oligomerization of styrene without using a Lewis acid. Oligomers and polymers with low degree of polymerization were obtained and characterized by GPC and NMR spectroscopy. Solvents and ligands have a strong effect on the catalyst activity, the molecular weight distributions and the polymer microstructure. The end groups were characterized in the case of the ligand‐free and the tributylphosphine and tricyclohexylphosphine‐modified systems. A terminal benzylidene group was observed except for the latter basic and bulky phosphine which led to a methylene terminal group. A mechanism involving a hydridonickel species is proposed.