Carbocyclic-fused N,N,N-pincer ligands as ring-strain adjustable supports for iron and cobalt catalysts in ethylene oligo-/polymerization

Abstract

Recent progress in the application of homogeneous iron and cobalt catalysts in ethylene oligo-/polymerization is reviewed with particular emphasis placed on the tuning of catalyst performance through the introduction of controlled amounts of ring strain to the ligand frame. While new examples of catalysts bearing the prototypical bis(arylimino)pyridine continue to emerge in the literature, the last decade has witnessed a number of key advances concerned with the fusion of carbocyclic units to the N,N,N-pincer manifold with a view to enhancing both the catalytic activities and thermal stability of their resultant catalysts. Some notable examples include iron complexes containing aryl-fused imino-phenanthroline ligands, which have proved highly active catalysts for ethylene oligomerization and indeed have shown considerable industrial promise on the pilot plant scale. Elsewhere, bis(arylimino)pyridines incorporating singly or doubly fused cycloalkyl units with the ring sizes anywhere between five-and eight-membered have been systematically developed and have proved versatile supports for both metal centers. More significantly, clear correlations between structure and activity as well as oligo-/polymer properties are a feature of these strain-adjustable catalysts. In many cases, linear vinyl-polyethylenes are accessible which are in demand for the production of long-chain branched copolymers, functional polymers as well as coating materials.

Extremely Active Ethylene Tetramerization Catalyst Avoiding the Use of Methylaluminoxane: [iPrN{P(C6H4‐p‐SiR3)2}2CrCl2]+[B(C6F5)4]−

“…Gratifyingly, the catalyst precursor prepared with [PhN(H)Me 2 ] + [B(C 6 F 5 ) 4 ] À and 2 according to the procedure shown in Scheme 1 was also as highly active as the one prepared with [H(OEt 2 ) 2 ] + [B (C 6 F 5 ) 4 ] À . The temperature rose from 30°C to 95°C in 15 min because of a large exotherm and the activity was calculated to be 5600 kg/g-Cr/h (entry 2 in Table 1 4 ] À (2.0 eq) overnight at room temperature, the solvent was changed from acetonitrile to CH 2 Cl 2 because 2 was insoluble in acetonitrile. Upon addition of 2 in CH 2 Cl 2 , the color immediately changed Scheme 1.…”

“…Preparation of the catalyst precursors discussed in a previous work. [46] 4 ] À (1.0 eq), CrCl 3 (THF) 3, and 2 were mostly soluble in methylcyclohexane. The methylcyclohexane-soluble portion (92 wt%) was taken by filtration for the use in the oligomerization studies.…”

“…Ethylene oligomerization catalysts typically generate 1-alkenes with an even number of carbon atoms such as 1-hexene, 1octene, 1-decene, etc., which are also called whole linear αolefins (LAOs). [1][2][3][4][5] 1-Hexene and 1-octene are used as comonomers in the ethylene polymerization processes, and their demand has increased with the increase in the production capacity of linear low-density polyethylene (LLDPE) and polyolefin elastomer (POE). Whereas nickel-and zirconium-based catalysts are used in the Shell higher-olefin process and Sabic/ Linde Alpha-SABLIN process, respectively, to produce a wide range of LAOs (Flory-Schulz distribution), [6,7] Cr-based catalysts that can selectively generate 1-hexene and/or 1-octene have also been discovered.…”

“…Catalyst development for ethylene oligomerization is an ongoing research topic in both academia and industry. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] 4 ] À (2.0 eq), CrCl 3 (THF) 3 , and PNP ligand that exhibited high activity (up to 4000 kg/g-Cr/h) when combined with common and inexpensive alkylaluminum iBu 3 Al (Scheme 1). [46] We presumed that the chloride-bridged adduct (i. e., [(PNP)Cr(Cl)(THF)(μ 2 -Cl) 2 Al(acac)] 2 + [B(C 6 F 5 ) 4 ] À 2 ) might be formed between the cationic Cr species [(PNP)CrCl 2 ] + [B(C 6 F 5 ) 4 ] À and the cationic Al species [ClAl(acac)] + [B(C 6 F 5 ) 4 ] À .…”

Pd‐Iminocarboxylate Complexes and Their Behavior in Ethylene Polymerization

“…[3] An ethylene dimerization Pd-phosphine-sulfonatec atalyst can be tweaked to yield high molecular weight PE. [5][6][7] Figure 1( D = Lewis base or ad onor atom/solvent) depicts some of the representative catalysts employedi nt he ethylene polymerization reaction. [5][6][7] Figure 1( D = Lewis base or ad onor atom/solvent) depicts some of the representative catalysts employedi nt he ethylene polymerization reaction.…”