N-Pyrrolyl-[N,N,N]-bis(imino)pyridyl iron(II) and cobalt(II) olefin polymerization catalysts

A series of new [N,N,N] 2,6‐bis(imino)pyridyl iron and cobalt halide complexes as precatalysts for the homo‐ and co‐polymerization of ethylene has been synthesized and evaluated for their catalytic performance. The novel key structural feature of these [N,N,N]MCl2 catalysts is their peripheral substitution with bulky N‐heterocyclic groups, including substituted N‐pyrrolyl, N‐indolyl, N‐carbazolyl, and N‐triazolyl moieties. The synthesis starts with the corresponding N‐amino‐N‐heterocycles, which were prepared by a modified Paal–Knorr condensation of 1,4‐diketones with mono‐protected hydrazines, or by electrophilic amination of benzannelated azoles. Condensation with 2,6‐diacetylpyridine or 2,5‐diformylthiophene afforded 14 different terdentate ligands, and complex formation with iron(II), iron(III), cobalt(II) yielded 23 different precatalysts. A single crystal structure analysis of one representative showed that these paramagnetic complexes have a distorted trigonal bipyramidal structure with orthogonal sterically shielding N‐azolyl groups. All the methylalumoxane‐activated iron(II) and cobalt(II) complexes with N‐pyrrolyl, N‐indolyl, and N‐carbazolyl substituents are highly active catalysts for the homo‐ and co‐polymerization of ethylene, producing polymers with comparatively narrow molecular weight distributions and with a wide range of molecular weights, dependent on the substitution pattern of the peripheral N‐azolyl substituents. The observed microstructures of the polymers vary from very highly branched to mostly linear, giving access to oligomers and polymers with an unusual broad spectrum of macroscopic physical properties. Copyright © 2002 John Wiley & Sons, Ltd.