Electronic and steric effects of amines on the dimerization of isoprene catalyzed by nickel complex

Abstract Electronic and steric effects of amines on the dimerization of isoprene catalyzed by bis-tri-phenylphosphinenickel (II) dichloride-NaBH4 have been studied from the viewpoint of substituent effects. Alkylamines accelerated the formation of linear dimers. The rates of DMOT formation were well correlated with the combination of σ ∗ and Es values of alkyl groups, indicating that the steric as well as electronic factors of the amines may play some roles in the catalytic process of the dimerization. Pyridine and its methyl-substituted derivatives accelerated the cyclic dimerization; however, the activity of γ-picoline was much larger than that of α-picoline, indicating again the importance of the steric effect of the amine. The roles of amine in the dimerization reaction are discussed in terms of the proposed mechanism.