Oligo or poly? A mechanistic interpretation of a switchable catalyst

It is not uncommon to find catalytic systems for which changes in the ligand environment - even apparently quite minor ones - bring about a complete switchover between olefin oligomerization and polymn., but explanations of such effects on a detailed structural and mechanistic level are not so common. We have found that activation of the dibenzylzirconium complex 1 by abstraction of a benzyl group in the absence or presence of an addnl. ligand L can generate a catalyst for oligomerization or polymn. of 1-hexene, or neither, depending on the mode of activation and the nature of L. From structural characterization of intermediates by NMR and X-ray crystallog. along with end-group anal. of oligomers and polymers, we can construct a mechanistic model that satisfactorily accounts for the variety of obsd. behaviors.