Syntheses of Ester-Substituted Norbornyl Palladium Complexes Ligated with ^tBu₃P: Studies on the Insertion of exo- and endo-Monomers in the Ester-Substituted Norbornene Polymerization

Exo- and endo-isomers of an ester-substituted norbornene derivative [5-norbornene carboxylic acid methyl ester (NBE)] are compared in the addition polymerization using ^tBu₃P-ligated palladium complex 1. The polymerization rate of endo-NBE is slower than that of the corresponding exo-NBE. Each of exo- and endo-NBE inserted complexes was synthesized and the insertion rate constant was determined for exo-NBE and endo-NBE. These experiments revealed that the consecutive exo-NBE insertion was faster than the consecutive endo-NBE insertion by 2-fold. On the other hand, in polymerization of an exo-NBE/endo-NBE (1:1) mixture, consumption rates of exo-NBE and endo-NBE were almost equal and the production rate of the poly-NBE from this mixture was almost the same as that of homopolymerization of exo-NBE.