Preparation and structures of aryloxy– and alkoxy–Ti(IV) complexes and their evaluation in ethylene oligomerisation and polymerisation

A range of aryloxy and alkoxy ligands, both monodenate and chelating, have been coordinated to Ti(IV) to yield complexes of the form [Ti(OAr)₂Cl₂], [Ti(RO^O)Cl₃] and [Ti(RO^O)₂Cl₂] (R = aryl, alkyl). The complexes vary in their Lewis base solvation and/or aggregation state, as revealed by X-ray crystallography of selected examples. The complexes have been evaluated as catalysts for ethylene oligomerisation and polymerisation following activation with alkylaluminium reagents (AlEt₃, methylaluminoxane). While polyethylene is the major product, ethylene oligomers also result, ranging from dimers to higher oligomers. The results indicate a number of different active species are formed upon activation, with oligomers likely arising through a metallacyclic mechanism. The findings are discussed in the context of the commercial Alphabutol dimerisation system [Ti(OR)₄], and the development of group 4 based ethylene trimerisation catalysts.