Oligomerization of 1-hexene initiated by Zr(OnPr)4-AlEt2Cl, 2. Mechanistic aspects

The mechanistic aspects of 1-hexene oligomerization, initiated by Zr(OnPr)₄-AlEt₂Cl at 20°C, are discussed on the basis of the product structures and distributions, the stability and reactivity of Mt-alkyls (Mt = metal) formed during 1-hexene oligomerization, the reaction behaviour of an internal olefin (cis-2-hexene) and the investigation of interactions between Zr (OnPr)₄-AlEt₂Cl. After comparing the different possible initation routes for 1-hexene oligomerization, a mechanism via insertion of 1-hexene into Al-alkyl bonds activated by zirconium is proposed. It was found that the olefin addition is not regiospecific. Primary addition into a linear alkyl-metal bond leads to an olefin insertion, whereas secondary addition only leads to elimination; when α- or β- branched alkyl-metal bonds are involved, only transfer to monomer takes place.