Oligomerization of Isoprene by Vanadium Catalysts

Oligomerization of isoprene by the catalyst system consisting of VO(OEt)3 and organoaluminum compounds was studied. Isoprene was oligomerized to a mixture of dimers, trimers and higher oligomers by VO(OEt)3–Et2AlCl catalyst system. 2,6-Dimethyl-1,trans-3,6-octatriene was the main dimer of isoprene in this reaction. The addition of tetrahydrofuran, dioxane, triphenylphosphine, bis-diphenylphosphinoethane, triethylamine or tetramethylethylenediamine to this catalyst system raised the reaction rate and the selectivity for the dimer at lower donor/VO(OEt)3 molar ratios but suppressed the reaction at higher molar ratios. By VO(OEt)3–Et3Al catalyst system, isoprene was converted to a liquid polymer and by VO(OEt)3–EtAlCl2 catalyst system, it was cyclopolymerized to an insoluble polymer. Structures of two new oligomers of isoprene were also reported.