New catalyst design for polymerization of norbornene esters by reducing intramolecular interaction.

We have used density functional theory to study palladium-based catalysts commonly used for the polymerization of norbornene derivatives with an ester group. Exo-exo, exo-endo, and endo-endo isomers of catalyst complexes were investigated; the endo-endo isomer was the most stable and inactive due to an intramolecular interaction between Pd and O of the carbonyl group. Phosphine groups are effective in minimizing the Pd-O interaction in the endo-endo isomer and P(C6H11)3 was found to be the most efficient reagent. The intramolecular Pd-O interactions were estimated using model complexes, and it was demonstrated that they play a crucial role in stabilizing the endo-endo isomer.