Preparation, Structure, and Ethylene Polymerization Behavior of Bis(imino)pyridyl Chromium(III) Complexes

The synthesis, characterization, and ethylene polymerization behavior of a family of chromium(III) complexes of formula [2,6-bis(imino)pyridyl]CrCl3 is reported. The X-ray diffraction studies of two of the new compounds show that the geometry around the chromium atom is octahedral, with the three chlorine ligands in a mer disposition. The distance between the metal and one of the trans-disposed chlorine atoms is significantly longer than the other two Cr−Cl distances. Treatment of the complexes [2,6-bis(imino)pyridyl]CrCl3 with methylaluminoxane (MAO) leads to very active ethylene polymerization catalysts that afford highly linear polyethylene. The substituents at the ortho position of the N-aryl groups of the 2,6-bis(imino)pyridyl ligands modulate both the catalytic activity and the molecular weights of the resulting polyethylene. The most active catalysts are those with two substituents at the ortho position of the N-aryl groups (activities up to 4 × 107 g (mol of Cr)-1 bar-1 h-1 are achieved). Regardin...