Arene substituted cyclopentadienyl complexes of Zr and Hf: preparation and evaluation as catalysts for ethylene trimerisation

A range of ZrIV and HfIV complexes of arene-substituted cyclopentadienyl ligands have been prepared and tested in ethylene oligomerisation. The complexes prepared were designed to be precatalysts to active species which have been predicted, through theoretical studies, to lead to selective ethylene trimerisation. While there is evidence for selective 1-hexene formation in the liquid fraction with two of the complexes, the major product in each case is polyethylene. Mechanistic studies reveal that trimerisation products most likely arise through a metallacycle mechanism, whereas there is evidence to suggest that polyethylene if formed via an alternate mechanism