Group 4 Metal Olefin Polymerization Catalysts Stabilized by Bidentate O,P Ligands

A series of bis(phosphanylphenoxide) group 4 metal dichloride complexes has been synthesized via treatment of MCl 4 (THF) 2 (M = Ti, Zr, Hf) with sodium salts of the phosphanylphenols. The complexes bearing diphenylphosphine donors adopt C 1 -symmetric, all- cis ground-state structures as determined by X-ray crystallography. In solution an O,P ligand exchange process is observed. Eyring analyses indicate a nondissociative process proposed to proceed via a 120° rotation of the P,P,Cl or the O,P,Cl trigonal faces. A zirconium complex containing diisopropylphosphine donors adopts a configurationally rigid trans -P 2 geometry. In ethylene polymerization studies (methylaluminoxane (MAO) activation), bis(6- tert -butyl-2-diphenylphosphanylphenoxide) zirconium and hafnium catalysts gave activities up to 49 000 and 2000 g/mmol·h·bar, respectively. Both of these catalysts also afforded efficient catalyzed chain growth using ZnEt 2 . The zirconium derivative afforded activities up to 13 300 g/mmol·h for propylene polymerization using “dried”-MAO (DMAO) as the cocatalyst. The polymer had a slight syndiotactic bias and is formed by a chain-end control mechanism. A dibenzyl analogue of the highly active zirconium catalyst revealed an all- cis structure by crystallography, but a mixture of isomers in solution by NMR spectroscopy. Cationic monoalkyl complexes were synthesized using either [CPh 3 ][B(C 6 F 5 ) 4 ] or DMAO and suggest a highly fluxional structure for the catalytically active species.