Iron and Cobalt Ethylene Polymerization Catalysts Bearing 2,6-Bis(Imino)Pyridyl Ligands:  Synthesis, Structures, and Polymerization Studies

Abstract

The synthesis, characterization, and ethylene polymerization behavior of a series of iron and cobalt halide complexes, LMX n (M ) Fe, X ) Cl, n ) 2, 3, X ) Br, n ) 2; M ) Co, X ) Cl, n ) 2), bearing chelating 2,6-bis(imino)pyridyl ligands L [L ) 2,6-(ArNCR 1 ) 2 C 5 H 3 N] is reported. X-ray diffraction studies show the geometry at the metal centers to be either distorted square pyramidal or distorted trigonal bipyramidal. Treatment of the complexes LMX n with methylaluminoxane (MAO) leads to highly active ethylene polymerization catalysts converting ethylene to highly linear polyethylene (PE). LFeX 2 precatalysts with ketimine ligands (R 1 ) Me) are approximately an order of magnitude more active than precatalysts with aldimine ligands (R 1 ) H). Catalyst productivities in the range 3750-20600 g/mmol‚h‚bar are observed for Fe-based ketimine catalysts, while Co ketimine systems display activities of 450-1740 g/mmol‚h‚bar. Molecular weights (M w ) of the polymers produced are in the range 14000-611000. Changing reaction conditions also affects productivity and molecular weight; in some systems, a bimodal molecular weight distribution is observed. On the basis of evidence gathered to date, the lower molecular weight fraction is a result of chain transfer to aluminum while the higher molecular weight fraction is produced by a combination of mainly -H transfer and some chain transfer to aluminum.

Synthesis and Evaluation of New Bis(imino) Pyridine Based Catalysts for Ethylene Polymerization

“…This result is consistent with that reported in the literature [14]. It is suggested that, for bulky catalysts larger amounts of MAO should be required.…”

“…After being stirred at 353 K for 15 min, the reaction was allowed to cool to room temperature. The obtained material was concentrated, and diethyl ether (30 ml) was added to precipitate the product as a blue powder, which was subsequently washed 3 times with diethyl ether (3x10 ml); after this, it was filtered and dried [14].…”

Distinguishing Chain Growth Mechanisms in Metal-catalyzed Olefin Oligomerization and Polymerization Systems: C2H4/C2D4 Co-oligomerization/Polymerization Experiments Using Chromium, Iron, and Cobalt Catalysts

“…[29][30][31] Chain growth with these catalysts is believed to occur via a Cossee-type mechanism whereby k p ≈ k t . Experimental evidence for the involvement of this mechanism was initially obtained from C 2 H 4 /C 2 D 4 co-oligomerization experiments using a bis(imino)pyrdine cobalt(I) chloride catalyst similar to 3, in combination with MAO.…”

Homo- and Co-polymerization of Ethylene with 1-Hexene Using Heterogeneous Catalysts Consisting of Bis(imino)pyridinevanadium Complex Supported on Clay Minerals and Alkyl Aluminum Compounds

“…These chemicals were dehydrated by passing them through a MS-13X column and were degassed by bubbling N2 before use. The bis(imino)pyridine derivatives (PBI-1 and -2) were prepared by the condensation reaction of 2,6-diacetylpyridine and substituted aniline according to a procedure described in the literature 3) . Triethylaluminum (TEA), diethylaluminum chloride (DEAC), and triisobutylaluminum (TIBA) as aluminum compounds were purchased from Kanto Chemical Co., Inc. MAO was obtained from the Sigma-Aldrich Corp.…”