Phosphanyl Methanimine (PCN) Ligands for the Selective Trimerization/Tetramerization of Ethylene with Chromium

Radcliffe, James E.; Batsanov, Andrei S.; Smith, David M.; Scott, John; Dyer, Philip W.; Hanton, Martin J.

doi:10.1021/acscatal.5b02106

Cited by 49 publications

(42 citation statements)

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“…However, too much ligand steric bulk could impede ethylene coordination to the catalyst. The correlation between catalytic activity and PE formation is also reflected in publications involving other bidentate ligand motifs as well as with tridentate ligands …”

Section: Resultsmentioning

confidence: 86%

Ethylene Tetramerisation: A Structure‐Selectivity Correlation

et al. 2020

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The effect of ethylene tetramerisation ligand structures on 1‐octene selectivity is well studied. However, by‐product formation is less understood. In this work, a range of PNP ligand structures are correlated with the full product selectivity and with catalyst activity. As steric bulk on the N‐substituent increases, the product selectivity shifts from >10 % to < 3% of both C6 cyclics and C16+ by‐products. 1‐Octene peaks at ca. 70%. Thereafter, only 1‐hexene increases. Similar selectivity changes were observed for ortho‐Ph‐substituted PNP ligands. The C10‐14 selectivity was less affected by the ligand structure. The ligand effect on the changes in selectivity is explained mechanistically. Lastly, an increase in ligand steric bulk was found to improve catalyst activity and reduce polymer formation by an order of magnitude. It is proposed that steric bulk promotes formation of cationic catalytic species which are responsible for selective ethylene oligomerisation.

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Section: Resultsmentioning

confidence: 86%

Ethylene Tetramerisation: A Structure‐Selectivity Correlation

et al. 2020

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“…7,8 Several chromium complexes have been reported that oligomerise ethylene with high selectivity to 1-hexene or 1-octene, for example those based on PNP ligands, [9][10][11][12] and more recently with PNC=N and PC=N ligand systems. 13,14 The trimerisation of ethylene to 1-hexene with a pyrrole/chromium-based catalyst is operated by the Phillips Petroleum Company, 15 and Sasol has recently commercialised a tri/tetramerisation technology based on PNP/chromium catalysts for the production of 1-hexene and 1-octene. 16 Some examples of commercial oligomerisation catalysts are collected in Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Alternating α-Olefin Distributions via Single and Double Insertions in Chromium-Catalyzed Ethylene Oligomerization

et al. 2016

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The catalytic oligomerization of ethylene with chromium-based complexes containing bis(benzimidazolemethyl)amine (BIMA) ligands results in alternating distributions of linear α-olefins (LAOs). Extremely high activities are obtained (>100 000 g mmol–1 h–1 bar–1) with N-alkyl-substituted BIMA ligands, whereas bulky groups on the central nitrogen or alternative central donors result in much lower activities. Variations in the ligand backbone, as well as methylation of the benzimidazole units, lead to reduction in activity. The alternating LAO distributions have been mathematically analyzed using second-order recurrence relations. The shape of the distributions is affected by ethylene pressure (1–4 bar) and by the cocatalyst to some degree. On the basis of the results and analysis presented herein, we propose that the alternating behavior originates from the ability of these chromium BIMA catalysts to undergo single as well as double ethylene insertion reactions. A minor second distribution (<5 wt %) of 2-ethyl-1-alkenes is obtained under certain conditions, resulting from incorporation of 1-butene. DFT studies (M06L) and experimental observations regarding the reaction between AlMe3 and the N-methyl BIMA ligand 2 have shown that deprotonation of the benzimidazole N–H units can occur, which suggests a change in coordination of the BIMA ligand under oligomerization conditions.

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“…Elsewhere, Cr(III) complexes coordinated by the diphosphinothiophenes 59a -59e ( Figure 21 Cr(acac)3 formed precatalysts that displayed TOFs of between 126900 and 312500 h -1 for ethylene oligomerization with 61c producing 1-hexene and 1-octene in a 2:1 ratio along with some polymer. The 1-phosphanyl methanimine P^N-ligands, 62a -62h ( Figure 21) have also emerged as compatible supports for chromium ethylene tri-/tetramerization catalysts [146] as have the phosphazane ligands 63a -63e ( Figure 21) [147]. For example, the chromium catalyst derived from N-cyclohexyl-containing 63e displayed a high activity of 316.7 kg (g Cr) −1 h −1 along with a high total selectivity of 85.1% towards 1hexene (45.7%) and 1-octene (39.4%).…”

Section: Bi-and Tridentate Ligands Based On P-and S-donors and Their mentioning

confidence: 99%

“…While homogeneous chromium catalysts have shown their importance in oligomerization and polymerization of ethylene (see section 2), they have also emerged as effective catalysts for the selective trimerization and more recently tetramerization of ethylene. Moreover, the products, 1-hexene and 1octene are in high demand due to their use as comonomers for the production of linear low-density polyethylene (LLDPE) [38,40,48,81,[131][132][133][134][135][136][137][138][139][140][141][142][143][144][145][146][147]. In this section, we again use the type of multidentate ligand to divide the sections with catalysts based on N^N^N discussed first before moving on to P^P, S^P^S, S^N^S, P^N^P and P^P^O systems.…”

Section: Chromium Catalysts For Selective Ethylene Trimerization and mentioning

confidence: 99%

Recent advances in homogeneous chromium catalyst design for ethylene tri-, tetra-, oligo- and polymerization

Bariashir

Huang

Solan

et al. 2019

Coordination Chemistry Reviews

112

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This review focuses on recent progress made using well-defined molecular chromium complexes that, upon suitable activation, can catalyze the tri-, tetra, oligo-and/or polymerization of ethylene. In particular, emphasis will be placed on the tuning of the performance characteristics of these homogeneous catalysts through structural modifications made to the multidentate ligand manifold (e.g., donor atoms, charge, backbone and strain) and the effects these changes have on the resulting ethylene derivatives. While the ability of these catalysts to mediate the formation of high molecular weight linear polyethylene continues to see many developments, their capacity to form polyethylene waxes and oligomers has witnessed some major advances. Moreover, the impressive selectivity of some chromium systems to generate commercially important 1-hexene and more recently 1-octene has seen the implementation of this technology at the industrial level. The types of precatalysts to be discussed will be divided broadly on the basis of their ability to generate either polymers/oligomers or short chain αolefins; the effects of co-catalyst and reaction conditions (e.g., temperature, pressure, solvent) on catalytic activity and selectivity, will be also developed. In addition, current proposals as to the mechanistic details displayed by these versatile chromium catalysts will be highlighted.

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Phosphanyl Methanimine (PCN) Ligands for the Selective Trimerization/Tetramerization of Ethylene with Chromium

Cited by 49 publications

References 50 publications

Ethylene Tetramerisation: A Structure‐Selectivity Correlation

Ethylene Tetramerisation: A Structure‐Selectivity Correlation

Alternating α-Olefin Distributions via Single and Double Insertions in Chromium-Catalyzed Ethylene Oligomerization

Recent advances in homogeneous chromium catalyst design for ethylene tri-, tetra-, oligo- and polymerization

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