Coordination compounds of titanium and zirconium with 6,6′-(piperazine-1,4-diyl)-bis-(2,4-di-tert-butylphenol) and study of their catalytic activity towards ethylene and 1-hexene polymerizations

•New Ti(IV) and Zr(IV) complexes based on [ONNO]2− ligand were synthesized.•The molecular structure of the complex 2 was determined by X-ray crystallography.•Complexes 2–3 are active in olefin polymerization only in the presence of Et2AlCl/Bu2Mg.•Ability of Mg derivatives to improve the catalytic ability was determined.

Novel titanium and zirconium alkoxo complexes bearing 6,6′-(piperazine-1,4-diyl)-bis-(2,4-di-tert-butylphenolate) ligand (L), LTi2(OiPr)6 (2) and L2Zr2(OBu)4 (3), has been synthesized in acceptable yields by the stoichiometric reaction of L with the respective M(OR)4. All complexes were fully characterized by elemental analysis and NMR spectroscopy, and the molecular structures of the representative complex 2 was confirmed as distorted trigonal bipyramid at titanium (coordination number 5) by single-crystal X-ray diffraction. Pre-catalysts 2–3 are active in ethylene and 1-hexene polymerization in the presence of Et2AlCl/Bu2Mg binary co-catalyst; but there were completely inactive in presence of MAO or Me3Al. Obtained polyethylene and polyhexene samples were of high molecular weight. The results of this study show the unique ability of Mg derivatives to improve the catalytic ability of post-metallocene pre-catalysts.

Graphical abstractNewly titanium(IV) and zirconium(IV) alkoxo complexes bearing 6,6′-(piperazine-1,4-diyl)-bis-(2,4-di-tert-butylphenolate) ligand were synthesized. The crystal structure of titanium complex 2 was determined by X-ray crystallography. Pre-catalysts 2–3 were completely inactive in olefin polymerization in the presence of MAO or Me3Al. Catalytic systems formed only in the presence of Et2AlCl/Bu2Mg binary co-catalyst.Figure optionsDownload full-size imageDownload as PowerPoint slide