Titanium complexes having chelating diaryloxo ligands bridged by tellurium and their catalytic behavior in the polymerization of ethylene

A series of titanium complexes having tellurium-bridged chelating bis(aryloxo) ligands, [TiX2{2,2'-Te(4-R-6-R'-C6H2O)(2)}](2) (5b, X = Cl, R Me, R' = Bu-t; 6a, X = (OPr)-Pr-i, R = R' = H; 6b, X = (OPr)-Pr-i, R = Me, R' =Bu-t), were prepared. 5b and 6b were determined by X-ray crystallography to have chloro- and isopropoxo-bridged dimeric structures. The structural data for these complexes indicated that the Ti-Te coordination bonds were stronger than the similar Ti-S coordination bonds in the corresponding sulfur-bridged complexes. The reaction of (C5R5)TiCl3 (R = H, Me) with 2,2'-Te(4-R-6-RI-C6H2OLi)(2) gave monocyclopentadienyl derivatives, (C5R5)TiCl{2,2'-Te(4-Me-6-Bu-t-C6H2O)(2)} (7, R = H; 8, R = Me). The monomeric four-legged piano-stool geometry of 8 was revealed by X-ray analysis. Upon addition of methylaluminoxane (MAO), these complexes catalyzed the polymerization of ethylene. The activities of the tellurium-bridged complexes were found to be significantly higher than those of the corresponding methylene-bridged complex.