Synthesis and ethylene polymerization behavior of {MeB(3-Ph-pyrazolyl)3}TiCl3

The new methyl-tris(pyrazolyl)borate reagents Li[MeTpPh] (1) [MeTpPh]− = MeB(3-Ph-pyrazolyl)3−) and Tl[MeTpPh] (2) react with TiCl4 to afford (MeTpPh)TiCl3 (3) in 77% and 81% yield respectively. 2 reacts with ZrCl4 and HfCl4 to yield mixtures of products. The reaction of 1 with TiCl3(THF)3 proceeds with B–N bond cleavage to afford TiCl3(3-Ph-pyrazole)(THF)2 as the major product (30%). The reaction of 3 with MeLi (3 equiv) yields 1 (60%) and reduced Ti species, via apparent displacement of [MeTpPh]− and generation of unstable TiCl4Me4−x species. Under MAO activation conditions (MAO = methylalumoxane), 3 polymerizes ethylene to linear polyethylene. 3/MAO is significantly more active in ethylene polymerization than the hydrido-tris(pyrazolyl)borate analogue {HB(3-Ph-pyrazolyl)3}TiCl3/MAO.