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

Abstract

AbstractA 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.