Chromium complexes bearing pyrazolyl-imine-phenoxy/pyrrolide ligands: Synthesis, characterization, and use in ethylene oligomerization

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A series of new Ni(II) complexes of general formula Ni{ZNO} Br (2a‐i) (ZNO = phenoxy/naphthoxy‐imine with pendant N‐ and O‐donor groups) were prepared and characterized by elemental analysis, IR spectroscopy, ESI‐HRMS, and by X‐ray crystallography for 2e. In the solid state, 2e features a monomeric structure with κ3 coordination of the monoanionic naphthoxy‐imine‐quinoline ligand onto the nickel center. Upon activation with MAO, both classes of nickel catalysts were able to produce selectively 1‐butene (81.5–92.1 wt%) with turnover frequencies (TOFs) varying from 3,100 to 24,300 mol(C2H4) mol (Ni)−1 h−1. Nickel precatalysts bearing phenoxy‐imine ligands were much more active than its naphthoxy analogous under the same conditions. The use of a mixture of cocatalysts (MAO/TMA or MAO/TiBA) resulted in poor activities; however the presence of TiBA in the milieu led to a significant improvement on selectivity for 1‐hexene (25.5 wt%). Under optimized conditions ([Ni] = 10 μmol, 30 °C, oligomerization time = 5 min, 20 bar ethylene, [Al]/[Ni] = 600), precatalyst 2c led to TOF = 59,900 mol(C2H4) mol(Ni)−1 h−1 and selectivity for 1‐butene of 89.5 wt%.

Section: Resultssupporting

confidence: 82%

Section: Methodsmentioning

confidence: 99%

Synthesis and characterization of Ni (II) complexes supported by phenoxy/naphthoxy‐imine ligands with pendant N‐ and O‐donor groups and their use in ethylene oligomerization

Oliveira

Silva

Casagrande

et al. 2018

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“…[4,5] Besides the choice of the metal center, various bi-and tridentate chelating ligands have been used to assist the generation and stabilization of the catalytically active specie. [7][8][9][10][11][12][13][14] Among the classes of pyrazolyl ligands, special attention has been devoted to those ones functionalized with different donor groups, mainly due to the structural diversity and ability to provide unusual and particular chemical reactivity. [6] In particular, pyrazolyl-based ligands and their metal complexes have been widely studied and applied in organometallic chemistry and homogeneous catalysis.…”

Section: Introductionmentioning

confidence: 99%

Pyrazolyl‐phosphinoyl nickel (II) complexes: synthesis, characterization and ethylene dimerization studies

Junges

Dresch

Costa

et al. 2019

A series of new nickel (II) complexes of general formula [NiBr 2 (N,O) 2 ] (Ni1-Ni5) based on bidentate pyrazolyl-phosphinoyl ligands were prepared and characterized by IR spectroscopy, elemental analysis, high-resolution mass spectrometry (HRMS), and X-ray crystallography for Ni1. X-ray crystallographic analyses of Ni1 revealed a six-coordinate species, in which Ni (II) lies in an octaedral environment. The nickel center is chelated by two pyrazolyl-phosphinoyl ligands with the two bromide ligands occupying mutually trans positions. Upon activation with methylaluminoxane (MAO), all nickel complexes were able to oligomerize ethylene with turnover frequencies (TOFs) varying from 5.0 to 16.6 × 10 3 (mol ethylene) (mol Ni) −1 h −1 producing selectively 1-butene (91.0-95.5 wt%). The substitution on the pyrazolyl group and the length of the backbone chain play a significant role in the catalytic activity. The use of MAO/TMA (1:1) or MAO/TiBA (1:1) instead of MAO drastically reduced the activities. The TMA content has no significant influence on the selectivity. However, the use of TiBA leads to a reduction of 1-butene (from 94.9 to 71.0 wt%) and an improvement in the hexene production (from 1.5 to 23.3 wt%). Under optimized reaction conditions (10°C, 20 min, 20 bar ethylene, [Al/Ni] = 600), Ni1/MAO catalytic system yielded TOF = 24.7 × 10 3 (mol ethylene) (mol Ni) −1 h −1 with good selectivities for α-C4 (94.9 wt%).

“…On elevating the oligomerization temperature from 80 to 100°C, the precatalyst still operated with good activity (62 700 (mol ethylene) (mol Cr) −1 h −1 ) with moderate selectivity for production of α‐olefins (66.2%) and only 1.1 wt% of the product formed was polyethylene. It should be pointed out that even at higher temperature (100°C), the 2c /MAO system was much more active than similar Cr(III) complexes such as [Cr{2‐(C 4 H 3 N‐2′‐CH═N)C 2 H 4 (NH)Ph}(THF)Cl 2 ] (TOF = 7100 (mol ethylene) (mol Cr) −1 h −1 ) and [Cr{5‐mesityl‐1‐pyrazolyl‐C 2 H 4 (N═CH)‐2,4‐ tert ‐butyl‐2‐(OH)C 6 H 2 }(THF)Cl 2 ] (TOF = 32 900 (mol ethylene) (mol Cr) −1 h −1 ) …”

Section: Resultsmentioning

confidence: 99%

“…In recent years, new classes of nickel and chromium complexes supported by Schiff base ligands containing furfural and pyrrolide groups have been synthesized and their catalytic application in ethylene oligomerization explored in detail . Studies revealed that the catalytic performances of these precatalysts are strongly affected by the nature of the heterocyclic moieties.…”

Section: Introductionmentioning

confidence: 99%

Chromium complexes based on thiophene–imine ligands for ethylene oligomerization

Ferreira

Zilz

Boeira

et al. 2019

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A new set of Cr(III) complexes, {L}CrCl3(THF), based on thiophene–imine (2a, L = PhOC6H4(N═CH)‐2‐SC4H3; 2b, L = PhOC2H4(N═CH)‐2‐SC4H3; 2c, L = Ph(NH)C2H4(N═CH)‐2‐SC4H3; 2d, L = PhOC6H4(N═CH)‐2‐SC4H2‐5‐Ph; 2e, L = Ph(NH)C2H4(N═CH)‐2‐SC4H2‐5‐Ph) have been prepared and characterized using elemental analysis and infrared spectroscopy. Upon activation with methylaluminoxane, all the chromium complexes generated active systems affording a nonselective distribution of α‐olefins with turnover frequencies in the range 9500–93 500 (mol ethylene) (mol Cr)−1 h−1, and producing mostly oligomers (95.0–99.3 wt% of total products). Small amounts of polymer were produced in these oligomerization reactions (0.8–8.2 wt%). The catalytic activities were quite sensitive to the ligand environment. Moreover, the effects of oligomerization parameters (temperature, [Al]/[Cr] molar ratio, time) on the activity and on the product distribution were examined.