Ethylene polymerization by palladium/phosphine-sulfonate catalysts in the presence and absence of protic solvents: Structural and mechanistic differences

Ethylene polymerization catalyzed by palladium(II)/ phosphine-sulfonate complexes was performed in the presence and absence of CH₃OHor CH₃OD. The addition of the protic solvents resulted in a significant decrease of molecular weight and a slight increase of internal alkene chain ends, suggesting that β-H elimination from alkylpalladiumintermediates was accelerated, which led to the following alkene dissociation from the Pd center or alkene isomerization. In the presence of CH₃OD, linear polyethylenes possessing deuteriums in the main chain were obtained presumably via a β-H elimination, H/D exchange, and reinsertion sequence.