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Ethylene Polymerization Behavior of Tris(pyrazolyl)borate Titanium(IV) Complexes

2002; American Chemical Society; Volume: 21; Issue: 9 Linguagem: Inglês

10.1021/om010530j

1520-6041

Shahid Murtuza, Osvaldo L. Casagrande, Richard F. Jordan,

Synthesis and characterization of novel inorganic/organometallic compounds

A set of Tp'TiCl3 and Tp'TiCl2(OR) complexes containing tris(pyrazolyl)borate ligands with diverse steric properties has been evaluated for ethylene polymerization under MAO activation conditions (Tp' = HB(3-mesitylpyrazolyl)2(5-mesitylpyrazolyl)- (TpMs*), HB(3-mesitylpyrazolyl)3 - (TpMs), HB(3,5-Me2-pyrazolyl)3 - (Τp*), HB(pyrazolyl)3 - (Tp), BuB(pyrazolyl)3 - (BuTp)). The activity of Tp'TiX3/MAO varies in the order TpMs*TiCl3 (10c) > TpMsTiCl3 ≫ Τp*TiCl3, TpTiCl3, BuTpTiCl3, Tp*TiCl2(OtBu), Tp*TiCl2(O-2-tBu-C6H4). The activity of 10c/MAO is similar to that of Cp2ZrCl2/MAO. High MAO levels or addition of AlMe3 decrease the activity of 10c/MAO, probably due to coordination of AlMe3 to the active Ti species. The predominant chain transfer mechanism for 10c/MAO is chain transfer to AlMe3, which results in broad molecular weight distributions at low Al/Ti ratios (Al/Ti = 200−1000). At very high Al levels (10c/5000 MAO or 10c/1000 MAO/4000 AlMe3) bimodal molecular weight distributions comprising a major low molecular weight fraction (M w/M n ca. 3) and a minor high molecular weight fraction are observed, which suggests that several active species are present, only one of which undergoes efficient chain transfer to Al.