Oligomerizations of Isoprene with Cobalt-complex Catalysts

Abstract

Oligomerizations of isoprene with the catalysts consisting of CoCl₂, NaBH_{4 and} Ph₃P in ethanol were investigated in detail.
A new 1, 3-coupled dimer of isoprene, 2, 3, 5-trimethyl-1, 4, 6-heptatriene [1], was mainly obtained when the molar ratio of Ph₃P to CoCl₂ was smaller than 1 (Table 1). But the two linear 4, 4- and 1, 4-coupled dimers, 2, 7-dimethyl-1, trans-3, 7-octatriene [3] and 2, 6-dimethyl-1, trans-3, 6-octatriene [4], were obtained when the molar ratio was larger than 1 (Table 2).
In both cases, some linear 1, 4- and 4, 4-coupled dimers, dimethyloctadienes, were also obtained. In these oligomerizations, in place of Ph₃P other trialkylphosphines (tri-n-butylphosphine and diethylphenylphosphine) and ditertiaryphosphine (bis-diphenylphosphinoethane) were studied as the ligands (Table 3 and 4). Furthermore, the solvent effect was also observed, that is, the cyclic dimers, 2, 4-dimethyl-4-vinyl-1-cyclohexene and dipentene (and/or diprene) were obtained by the use of the aprotic solvent such as toluene (Table 5).