Synthesis and characterization of iron, cobalt and nickel complexes bearing para-phenylene-linked pyridine imine ligand and their catalytic properties for ethylene oligomerization
“…The complex formation between the Zn(II) and HDPBA results in bathochromic shift of n-π* transition of the C=N functional group in HDPBA. Similar shifts of n-π* transition absorption band of other ligands upon complex formation with other metals have also been reported [ 32 , 33 , 34 , 35 ]. Fig.…”
“…The complex formation between the Zn(II) and HDPBA results in bathochromic shift of n-π* transition of the C=N functional group in HDPBA. Similar shifts of n-π* transition absorption band of other ligands upon complex formation with other metals have also been reported [ 32 , 33 , 34 , 35 ]. Fig.…”
“…This implies that the activities offered by cobalt complexes ( Run 1 , 3 , Table 6) are generally lower than those of their nickel analogues ( Run 3 , 5 , Table 6), while the same conclusion is reached in a study by Cao [34] . It shows that different metal atoms have different electronic effects [32] …”
Section: Resultsmentioning
confidence: 60%
“…The metal centers have a significant effect on the activity of corresponding catalysts [32,33] . From the crystallographic data and Table 6, it can be concluded that nickel complex 2 containing the same ligand L1 has higher activity than the corresponding cobalt complex 1 a .…”
Here, L1 (2-(pyridin-2-yl)quinoxaline) and L2 ((1-((1H-pyrrol-2yl)ethylidene)benzene-1,2-diamine) ⋅ (1-(1H-pyrrol-2yl)ethanone)) were synthesized and reacted with CoCl 2 ⋅ 6H 2 O and NiCl 2 ⋅ 6H 2 O to produce complexes 1-4. We found several interesting pieces of crystal structure information. Firstly, ligands L1 and L2 with completely different molecular structures were obtained by reacting the precursors containing similar N-heterocycles with 1,2-diaminobenzene. Secondly, in methanol and DMF solvents, 1 showed two structures, the binuclear and mononuclear cobalt complexes 1 a and 1 b.Finally, the structure of 4 showed the formation of a new 2 : 1 type ligand at eutectic L2 in the presence of a Ni 2 + template. Upon treatment with AIBN, 1-4 showed moderate to high activities for MMA polymerization, producing PMMA with low to high molecular weights (2.02 ∼ 73.03 × 10 4 g⋅mol -1 ) and moderate dispersity indices (PDI: 1.72 ∼ 3.32). Moreover, 1 b displayed higher catalytic activities (up to 1.138 × 10 5 g mol À 1 ⋅ h À 1 ), which was 20 times higher than that of 3 and more than 7 times higher than that of 1 a.
“…The selectivity of complexes 42 and 43 remained the same, with about 70% selectivity for C 4 . Wang et al [137] synthesized N,N-bidentate iron, nickel, and cobalt complexes bearing (6E,7E)-N 1 ,N 4 -bis((pyridin-2-yl)methylene)benzene-1,4-diamine ligands and investigated their ethylene oligomerization potential. The selectivity toward 1-hexene for cobalt complex 44 was usually higher than that of the iron or nickel complexes at 40 bar pressure.…”
Linear α-olefins (LAOs) are linear alkenes with double bonds at the ends of the molecular chains. LAOs with different chain lengths can be widely applied in various fields. Ethylene oligomerization has become the main process for producing LAOs. In this review, different homogeneous or heterogeneous catalysts recently reported in ethylene oligomerization with Ni, Fe, Co, Cr, etc., as active centers will be discussed. In the homogeneous catalytic system, we mainly discuss the effects of the molecular structure and the electronic and coordination states of complexes on their catalytic activity and selectivity. The Ni, Fe, and Co homogeneous catalysts are discussed separately based on different ligand types, while the Cr-based homogeneous catalysts are discussed separately for ethylene trimerization, tetramerization, and non-selective oligomerization. In heterogeneous catalytic systems, we mainly concentrate on the influence of various supports (metal–organic frameworks, covalent organic frameworks, molecular sieves, etc.) and different ways to introduce active centers to affect the performance in ethylene oligomerization. Finally, a summary and outlook on ethylene oligomerization catalysts are provided based on the current research. The development of highly selective α-olefin formation processes remains a major challenge for academia and industry.
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