Highly Regioselective α-Olefin Dimerization Using Zirconium and Hafnium Amine Bis(phenolate) Complexes

Abstract

Five new structural analogues of a previously studied group IV amine bis(phenolate) catalyst, Zr(ONNEt2O)Bn2, have been synthesized and tested for oligomerization activity. These structural variations encompass longer alkyl groups, propyl and butyl, on the pendant amine group and two different group IV metals, zirconium and hafnium. Remarkably, all five precatalysts, combined with tris(pentafluorophenyl)borane, oligomerized 1-hexene with almost exclusive selectivity for vinylidene end-groups with a marked preference for dimer formation. The three zirconium amine bis(phenolate) catalysts produced a Schulz–Flory distribution of oligomer products whereas the product distributions of the three hafnium analogues were seen to deviate from a Schulz–Flory distribution. The possible structures for dimers and trimers have been elucidated based on end-group and active site distribution.