Oligomerization and polymerization of 5-ethylidene-2-norbornene by cationic palladium and nickel catalysts

Nickel- and palladium-based catalyst systems were developed to convert 5-ethylidene-2-norbornene (ENB) to oligomers and polymers with highly controllable molecular weights. Depending on the choice of central metal ion, supporting ligand, and alpha-olefin chain transfer agent (CTA), ENB-derived materials ranging from dimers (ca. 270 Da) to high molecular weight polymers (>100 000 Da) were prepared. Typical reactions utilized [(eta(6)-mesitylene)M(eta(3)-2-R-allyl)](+) (M = Pd, R = H; M = Ni, R = Me) in dichloromethane solution at ambient temperature, with tertiary phosphine co-ligands and alpha-olefins controlling the enchainment. Access to oligomers of cycloolefins with M-n < 2000 Da is noteworthy, particularly considering that ENB is much less reactive than norbornene itself.