Steric and electronic effects in ethene/norbornene copolymerization by neutral salicylaldiminato-ligated palladium(II) catalysts

Three palladium(II) catalysts, ligated with naphthoxyimine ligands, were synthesized, structurally characterized, and used to copolymerize ethene with norbornene derivatives. Results show that modification of the functional group on the 8-carbon of the naphthol ligand can significantly influence polymer composition and structure. The three functional groups on the 8-carbon studied were -H (catalyst A), -OH (catalyst B), and -OCH₃ (catalyst C). Of the three catalysts, A is the most active toward ethene/5-n-butyl-2-norbornene and ethene/5-n-hexyl-2-norbornene copolymerizations; the molecular weight of the copolymers produced by catalyst A is significantly higher than those produced by either B or C. Both A and B are also capable of producing appreciable amounts of ethene/tert-butyl 5-norbornene-2-carboxylate copolymers which contain over 30% of the functionalized norbornene. C, in contrast to both A and B, is incapable of copolymerizing functionalized norbornene and ethene.