Zirconocene-alumoxane (1:1) -: a catalyst for the selective dimerization of α-olefins

A well known catalytic system for the oligomerization of 1-alkenes is zirconocene dichloride (Cp2ZrCl2,), when activated by a large excess of methylalumoxane (MAO). Surprisingly, when activated by only 1 equiv. of MAO, Cp2ZrCl2, selectively and catalytically dimerizes alpha-olefins without formation of any higher oligomeric species. This reaction is shown to be general for a number of alpha-olefins. The conversion of o-diallylbenzene gives a seven-membered cyclic product in an intramolecular dimerization reaction. A possible mechanism for the dimerization process involving a zirconium-hydrido species as the catalyst is formulated, and evidence for it is given by detection of by-products and a deuteration experiment. (C) 1998 Elsevier Science S.A.