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.