A family of zirconium complexes having two phenoxy-imine chelate ligands for olefin polymerization

A zirconium complex having two phenoxy-imine chelate ligands, bis[N-(3-tert -butylsalicylidene)anilinato] zirconium(IV)dichloride (1), was found to dis play a very high ethylene polymerization activity of 550 kg of polymer/mmol of cat(.)h with a viscosity average molecular weight (M-v) value of 0.9 x 10(4) at 25 degreesC at atmospheric pressure using methylalumoxane (MAO) as a cocatalyst. This activity is 1 order of magnitude larger than that exhib ited by Cp2ZrCl2 under the same polymerization conditions. The use of Ph3CB (C6F5)(4)/i-Bu3Al in place of MAO as a cocatalyst resulted in extremely hig h molecular weight polyethylene, M-v 505 x 104, with an activity of 11 kg o f polymer/mmol of cat h at 50 degreesC. This M, value is one of the highest values displayed by homogeneous olefin polymerization catalysts. Complex 1 , using Ph3CB(C6F5)(4)/i-Bu3Al as a cocatalyst, provided a high molecular w eight ethylene-propylene copolymer, M-v 109 x 10(4), with 8 kg of polymer/m mol of cat h activity at a propylene content of 20.7 mol %. X-ray analysis revealed that complex 1 adopts a distorted octahedral coordination structur e around the zirconium metal and that two oxygen atoms are situated in tran s position while two nitrogen atoms and two chlorine atoms are situated in cis position. DFT calculations suggest that the active species derived from complex 1 possesses two available cia-located sites for efficient ethylene polymerization. Changing the tert-butyl group in the phenoxy benzene ring enhanced the polymerization activity. Bis[N-(3-cumyl-5-methylsalicylidene)c yclohexylaminato] zirconium(IV)dichloride (7) with MAO displayed an ethylen e polymerization activity of 4315 kg of polymer/mmol of cat h at 25 degrees C at atmospheric pressure. This activity corresponds to a catalyst turnover frequency (TOF) value of 42 900/s(.) atm. This TOF value is one of the lar gest not only for olefin polymerization but also for any known catalytic re action. Ligands with additional steric congestion near the polymerization r eaction center gave increased M, values. The maximum M, value, 220 x 104 us ing MAO, was obtained with bis[N-(3,5-dicumylsalicylidene)2 ' -isopropylani linato]zirconium(IV)dichloride (15). Thus, polyethylenes ranging from low t o exceptionally high molecular weights can be obtained from these zirconium complexes by changing the ligand structure and the choice of cocatalyst.