Chromium(III) complexes bearing bis(benzotriazolyl)pyridine ligands: synthesis, characterization and ethylene polymerization behavior

Reaction of benzotriazole with 2,6-bis(bromomethyl)pyridine and 2,6-pyridinedicarbonyl dichloride yields the tridentate ligands 2,6-bis(benzotriazol-1-ylmethyl)pyridine (1) and 2,6-bis(benzotriazol-1-ylcarbonyl) pyridine (2). The molecular structures of the ligands were determined by single-crystal X-ray diffraction. These ligands react with CrCl3(THF)(3) in THF to form neutral complexes, [CrCl3{2,6-bis(benzotriazolyl)pyridine-N,N,N}] (3, 4), which are isolated in high yields as air stable green solids and characterized by mass spectra (ESI), FTIR spectroscopy, UV-Visible, thermogravimetric analysis (TGA), and magnetic measurements. After reaction with methylaluminoxane (MAO), the chromium(III) complexes are active in the polymerization of ethylene showing a bimodal molecular weight distribution. A DFT computational investigation of the polymerization reaction mechanism shows that the most likely reaction pathway originates from the mer configuration when the spacer is CH2 (complex 3) and from the fac configuration when the spacer is CO (complex 4). [GRAPHICS]