Titanium Complexes Stabilized by Bulky Electron-Rich Aminopyridinates and Their Application in Ethylene and Styrene Polymerization



A series of electron-rich aminopyridines with high electron density at the Npyridine atom (due to an electron-donating mesomeric effect) was prepared by the Ni0/2,2′-bipyridine-catalyzed arylation of anilines, followed by an uncatalyzed amination reaction. Reacting 2,6-dichloropyridine with 1 equiv. of aniline in the presence of the Ni0/2,2′-bipyridine catalyst gave exclusively N-(6-chloropyridin-2-yl)aniline. Subsequent reaction with secondary alkylamines provided electron-rich aminopyridines in which the lone pair of the RR′N substituent participates in the molecular π-system. These aminopyridines react with [Et2NTiCl3] (Et = ethyl) and undergo amine elimination to form simultaneously the corresponding aminopyridinate (Ap) ligand-stabilized titanium trichlorides [ApTiCl3] and Ap (diethylamido)titanium dichlorides [Ap(Et2N)TiCl2]. The reaction presumably proceeds via the reaction of the initially formed [ApTiCl3] with 2 equiv. of the prereleased diethylamine to give the [Ap(Et2N)TiCl2] complexes and diethylammonium chloride. Alternative selective synthetic routes for both sorts of complexes are also presented. These compounds were characterized by spectroscopic methods and X-ray diffraction analysis (selected complexes). Furthermore, their behavior in ethylene and styrene polymerization reactions was explored. The complexes show high activity towards ethylene if activated with d-MAO (‘‘dry” methylaluminoxane) but were almost inactive if d-MAO was replaced with conventional MAO. The observed polyethylene (PE) product was analyzed by NMR spectroscopy and found to be fully saturated, indicating a chain transfer reaction to aluminum had occurred. Styrene waspolymerized in a highly syndiospecific fashion.