Metallocene analogues containing bulky heteroallylic ligands and their use as new olefin polymerization catalysts

Abstract

A series of Ti and Zr metallocene analogues containing bulky benzamidinate ligands has been prepared and fully characterized. Treatment of TiCl 4(THF) 2 or ZrCl 4(THF) 2 with two equivalents of the appropriate benzamidinate anions affords the bis(benzamidinato) complexes [C 6H 5C(NC 3H 7) 2] 2MCl 2 (M=Ti ( 1), Zr ( 2)) and [C 6H 5C(NC 6H 11) 2] 2MCl 2 (M=Ti ( 3), Zr ( 4)). The zirconium complex 2 was structurally characterized by X-ray diffraction. In a similar manner the nonafluoromesityl derivative [(CF 3) 3C 6H 2C(NC 6H 11) 2] 2ZrCl 2 ( 5) was synthesized from ZrCl 4(THF) 2 and Li[(CF 3) 3C 6H 2C(NC 6H 11) 2]. Methylation of 4 with methyllithium yields the dimethyl complex [C 6H 5C(NC 6H 11) 2] 2ZrMe 2 ( 6). The mixed-ligand metallocene analogues [C 6H 5C(NC 3H 7) 2](C 5Me 5)MCl 2 (M=Ti ( 7), Zr ( 8)) and [C 6H 5C(NC 6H 11) 2](C 5Me 5)TiCl 2 ( 9) have been prepared by reacting (C 5Me 5)TiCl 3 or (C 5Me 5)ZrCl 3 with one equivalent of a lithium N, N″-dialkylbenzamidinate. The polymerization of ethylene and propylene has been studied by the catalytic precatalyst complexes 1 and 2 upon reaction of an excess of methylalumoxane to obtain the active cationic complexes. The polymerization activity of the complexes is comparable to other benzamidinate ancillary containing ligands although toward shorter amounts of time due to a competitive inhibition presumably obtained by a β-hydrogen elimination from the ligand. Polymerization activity is strongly dependent on catalyst and cocatalyst concentrations and on temperature.