Novel titanium(iv) complexes with 2,4-di-tert-butyl-6-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)phenol in ethene polymerization

Dinuclear (2) and mononuclear dichloride complexes (3) of titanium(iv) isopropoxide with a bidentate phenol alcohol ligand, viz., 2,4-di-tert-butyl-6-(1,1,1,3,3,3-hexafluoro-2-hydroxy-propan-2-yl)phenol, were obtained. The structures of the complexes were confirmed by X-ray diffraction. The dimeric structure of complex 2 is typical of alkoxy compounds and contains the bridging fragment Ti(mu-OPri)(2)Ti; the coordination polyhedron of the Ti atom is a distorted tetragonal pyramid. In complex 3, the Ti atom has a distorted octahedral environment made up of the O atoms of the ligand, the Cl atoms, and the O atoms of two coordinated propan-2-ol molecules. The catalytic properties of complexes 2 and 3 in ethene polymerization were studied with such promoters as polymethylaluminoxane (MAO), trimethylaluminum, triisobutylaluminum, diethylaluminum chloride, and Et2AlCl-MgBu2. Both the complexes were catalytically active (635 and 540 kg of polyethylene (PE)/(mol of Ti) h atm, respectively) only in the presence of the binary promoter Et2AlCl-MgBu2. The dichloride complexes obtained from a lithium or magnesium salt of the same ligand and TiCl4 without separation from lithium and magnesium chlorides formed as by-products were catalytically active in the presence of MAO, Bu-i Al-3, and Me3Al. For the catalytic system containing the dichloride complex and MgCl2, the best promoter is Me3Al (1082 kg of PE/(mol of Ti) h atm). The polymer obtained on all the catalytic systems is linear polyethylene characterized by high molecular weight (M-w = = 593900-2000000 g mol(-1)) and high polydispersity indices (M-w/M-n = 2.8-15). Various conjectures were made about why lithium and magnesium chlorides have the promoting effects.