Further studies on the effects of substituents at the Cp and salicyladiminato ligands of half-sandwich chromium(III) complexes on their catalytic properties for ethylene polymerization

Abstract

A series of new half-sandwich chromium(III) complexes Cp′[2-R1-6-(CHNR2)C6H2O]CrCl [R1 = iPr (1), tBu (2, 3, 4, 5); R2 = iPr (2, 4, 5), tBu (1, 3); Cp′ = C5H5(1, 2, 3), C5H2Ph3 (4), C5Me4Ph(5)] were synthesized from the reactions of Cp′CrCl2(THF) with corresponding salicyladiminato lithium. All complexes were characterized by elemental analyses and the structures of complexes 1, 2, 3 and 5 were determined by X-ray diffraction analysis. These complexes show moderate catalytic activities for ethylene polymerization upon activation with a relatively small amounts of AlMe3 or AlEt3, producing high molecular weight polyethylene in the form of spherical particles. Under similar conditions, the catalytic activity of complexes carrying a same salicylaldiminato ligand changes with the cyclopentadienyl ligand in the order Me5Cp > Me4PhCp > 1,2,4-Ph3Cp > Cp. The catalytic activity of these catalysts is also affected significantly by the AlR3 cocatalyst in the order AlMe3 > AlEt3.