Iminopyridine Complexes of 3d Metals for Ethylene Polymerization: Comparative Structural Studies and Ligand Size Controlled Chain Termination

Abstract

A variety of iron complexes bearing tridentate pyridine based ligands are presented as highly active precatalysts for the oligomerization and polymerization of ethene and propene. The ligands comprise two classes: the first class, where both ketone groups of the 2,6-diacetylpyridine are converted to imines to give symmetrical or unsymmetrical bis(imino)pyridines (NNN ligands; 1−4, 8, and 9), and the second class, where only one keto function of the 2,6-diacetylpyridine is substituted by an imine to give monoiminoacetylpyridines (NNO or MIAP ligands; 5−7). The NNN ligands have been reacted with FeCl2·4H2O to afford the corresponding metal complexes (12−17). These complexes have been activated by modified methylaluminoxane (MMAO) and tested in the oligomerization and polymerization reaction of ethene and propene. Depending on the steric bulk of the ortho substituents at the aryl group of the imines, tunable polymerization products are observed, with molecular weights (Mw) of 102−106. Using the MIAP ligands...