2‐Benzoxazolyl‐6‐[1‐(arylimino)ethyl]pyridyliron(II) Chlorides as Ethylene Oligomerization Catalysts

Abstract

A series of iron(II) dichloride complexes (Fe 1 –Fe 7 ) ligated by 2-(2-benzoxazolyl)-6-[1-(arylimino)ethyl]pyridines was synthesized and characterized [aryl = 2,6-R12C6H3; R1 = Me ( 1 ), Et ( 2 ), iPr ( 3 ), Cl ( 4 ), Br ( 5 ); 2,6-Me2C6H2-4-R2, R2 = Me ( 6 ), Br ( 7 )]. The molecular structures of Fe 1 , Fe 3 , and Fe 5 were determined by the single-crystal X-ray diffraction. Complexes Fe 1 and Fe 3 both display distorted trigonal-bipyramidal geometries, whereas complex Fe 5 is a distorted square pyramid. Upon activation with modified methylaluminoxane, all iron complexes showed moderate to good activities [up to ca. 106 g(product)?×?(mol Fe)–1 h–1?bar–1] for the oligomerization and polymerization of ethylene, with high selectivity for vinyl-terminated oligomers or polyethylene waxes

2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)ethyl]-6-[1-aryliminoethyl]pyridyl cobalt dichlorides: Synthesis, characterization and ethylene polymerization behavior

“…The analogous iron pre-catalysts generally performed with higher activities and produced more polyethylene than did their cobalt analogs. However, in the case of pre-catalysts bearing 2-benzoxazolyl-6-iminopyridines, the cobalt pre-catalysts were shown to exhibit an interesting temperature-switch feature for ethylene reactivity, producing 1-butene below 40 C and favoring ethylene polymerization at elevated temperatures [46]; the iron analogs mainly gave oligomers and small amounts of waxes [47]. Moreover, this finding was contrary to the common thinking that elevated reaction temperatures result in lower activities and produce lower molecular weight polyethylene products.…”

“…Driven by the hypothesis that N^N^N tridentate ligands would provide suitable iron(II) and cobalt(II)-based pre-catalysts [28e35], numerous heterocyclic compounds, which act as tridentate ligands, have been developed in our group. These include 2-imino-1,10-phenanthrolines [36e40], 2-(benzoxazolyl)-1,10-phenanthrolines [41], 2-(2-benzimidazolyl)-1,10-phenanthrolines [42], 2-benzimidazolyl-6-iminopyridines [43e45], 2-benzoxazolyl-6-iminopyridines [46,47], 2-quinoxalinyl-6-iminopyridines [48], N-((pyridin-2-yl)methylene)-8-aminoquinolines [49], 8-(1H-benzimidazol-2-yl)quinolines [50], as well as the 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines for bimetallic pre-catalysts [51,52]. In addition, several types of iron and cobalt complexes bearing bidentate ligands showed promise in ethylene polymerization or oligomerization [53e55].…”

Iron(II) and cobalt(II) complexes bearing 8-(1-aryliminoethylidene) quinaldines: Synthesis, characterization and ethylene dimerization behavior

“…Our group has recently reported a series of complexes with good to high activities for ethylene polymerization and oligomerization. These systems utilize newly developed ligands (Scheme 1) such as 2-imino-1,10-phenanthrolines (B) [23e30], 2-(benzoimidazolyl)-6-iminopyridines (C) [31,32], 2-quinoxalinyl-6-iminopyridines (D) [33,34], 2-(benzimidazol-2-yl)-1,10-phenanthrolines (E) [35,36], 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines (F) [37,38], N-((pyridin-2-yl)methylene)-quinolin-8-amine (G) [39], 2-benzoxazolyl-6-[1-(arylimino)ethyl]pyridines (H) [40], 2-oxazoline-or benzoxazole-1,10-phenanthrolines (I) [41], 2-(1-aryliminopropylidene)quinolines (J) [42], 2,8-bis(imino)quinolines (K) [43] and 2-[1-(2,6-dibenzhydryl-4-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridines [44]. Moreover, a number of the Fe(II) and Co(II) catalysts were capable of ethylene oligomerization with high activities and high selectivity of a-olefins, and can thus be considered as promising catalysts for industrial consideration.…”

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

“…In fact, it has been shown that the size, nature and regiochemistry of the substituents in the iminoaryl groups are extremely important in controlling the polymerization and oligomerization of ethylene [9,10]. Iron complexes bearing small substituents at the 2-positions of the aryl groups proved to be excellent catalyst precursors for oligomerization of ethylene.…”