MAO-free and extremely active catalytic system for ethylene tetramerization

Tae Hee Kim, Hyun Mo Lee, Hee Soo Park, Sung Dong Kim, Su Jin Kwon, Atsushi Tahara, Hideo Nagashima, Bun Yeoul Lee

Research output: Contribution to journalArticle

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Abstract

The original Sasol catalytic system for ethylene tetramerization is composed of a Cr source, a PNP ligand, and MAO (methylaluminoxane). The use of expensive MAO in excess has been a critical concern in commercial operation. Many efforts have been made to replace MAO with non-coordinating anions (e.g., [B(C 6 F 5 ) 4 ] ); however, most of such attempts were unsuccessful. Herein, an extremely active catalytic system that avoids the use of MAO is presented. The successive addition of two equivalent [H(OEt 2 ) 2 ] + [B(C 6 F 5 ) 4 ] and one equivalent CrCl 3 (THF) 3 to (acac)AlEt 2 and subsequent treatment with a PNP ligand [CH 3 (CH 2 ) 16 ] 2 C(H)N(PPh 2 ) 2 (1) yielded a complex presumably formulated as [1-CrAl (acac)Cl 3 (THF)] 2+ [B(C 6 F 5 ) 4 ] 2 , which exhibited high activity when combined with iBu 3 Al (1120 kg/g-Cr/h; ~4 times that of the original Sasol system composed of Cr (acac) 3 , iPrN(PPh 2 ) 2 , and MAO). Via the introduction of bulky trialkylsilyl substituents such as –SiMe 3 , –Si(nBu) 3 , or –SiMe 2 (CH 2 ) 7 CH 3 at the para-position of phenyl groups in 1 (i.e., by using [CH 3 (CH 2 ) 16 ] 2 C(H)N[P(C 6 H 4 -p-SiR 3 ) 2 ] 2 instead of 1), the activities were dramatically improved, i.e., tripled (2960–3340 kg/g-Cr/h; more than 10 times that of the original Sasol system). The generation of significantly less PE (<0.2 wt%) even at a high temperature is another advantage achieved by the introduction of bulky trialkylsilyl substituents. NMR studies and DFT calculations suggest that increase of the steric bulkiness on the alkyl-N and P-aryl moieties restrict the free rotation around (alkyl)N–P (aryl) bonds, which may cause the generation of more robust active species in higher proportion, leading to extremely high activity along with the generation of a smaller amount of PE.

Original languageEnglish
Article numbere4829
JournalApplied Organometallic Chemistry
Volume33
Issue number4
DOIs
Publication statusPublished - Apr 1 2019

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Ligands
Discrete Fourier transforms
Anions
Nuclear magnetic resonance
Temperature
ethylene
tris(acetylacetonato)chroum(III)

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Inorganic Chemistry

Cite this

Kim, T. H., Lee, H. M., Park, H. S., Kim, S. D., Kwon, S. J., Tahara, A., ... Lee, B. Y. (2019). MAO-free and extremely active catalytic system for ethylene tetramerization. Applied Organometallic Chemistry, 33(4), [e4829]. https://doi.org/10.1002/aoc.4829

MAO-free and extremely active catalytic system for ethylene tetramerization. / Kim, Tae Hee; Lee, Hyun Mo; Park, Hee Soo; Kim, Sung Dong; Kwon, Su Jin; Tahara, Atsushi; Nagashima, Hideo; Lee, Bun Yeoul.

In: Applied Organometallic Chemistry, Vol. 33, No. 4, e4829, 01.04.2019.

Research output: Contribution to journalArticle

Kim, Tae Hee ; Lee, Hyun Mo ; Park, Hee Soo ; Kim, Sung Dong ; Kwon, Su Jin ; Tahara, Atsushi ; Nagashima, Hideo ; Lee, Bun Yeoul. / MAO-free and extremely active catalytic system for ethylene tetramerization. In: Applied Organometallic Chemistry. 2019 ; Vol. 33, No. 4.
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abstract = "The original Sasol catalytic system for ethylene tetramerization is composed of a Cr source, a PNP ligand, and MAO (methylaluminoxane). The use of expensive MAO in excess has been a critical concern in commercial operation. Many efforts have been made to replace MAO with non-coordinating anions (e.g., [B(C 6 F 5 ) 4 ] − ); however, most of such attempts were unsuccessful. Herein, an extremely active catalytic system that avoids the use of MAO is presented. The successive addition of two equivalent [H(OEt 2 ) 2 ] + [B(C 6 F 5 ) 4 ] − and one equivalent CrCl 3 (THF) 3 to (acac)AlEt 2 and subsequent treatment with a PNP ligand [CH 3 (CH 2 ) 16 ] 2 C(H)N(PPh 2 ) 2 (1) yielded a complex presumably formulated as [1-CrAl (acac)Cl 3 (THF)] 2+ [B(C 6 F 5 ) 4 ] − 2 , which exhibited high activity when combined with iBu 3 Al (1120 kg/g-Cr/h; ~4 times that of the original Sasol system composed of Cr (acac) 3 , iPrN(PPh 2 ) 2 , and MAO). Via the introduction of bulky trialkylsilyl substituents such as –SiMe 3 , –Si(nBu) 3 , or –SiMe 2 (CH 2 ) 7 CH 3 at the para-position of phenyl groups in 1 (i.e., by using [CH 3 (CH 2 ) 16 ] 2 C(H)N[P(C 6 H 4 -p-SiR 3 ) 2 ] 2 instead of 1), the activities were dramatically improved, i.e., tripled (2960–3340 kg/g-Cr/h; more than 10 times that of the original Sasol system). The generation of significantly less PE (<0.2 wt{\%}) even at a high temperature is another advantage achieved by the introduction of bulky trialkylsilyl substituents. NMR studies and DFT calculations suggest that increase of the steric bulkiness on the alkyl-N and P-aryl moieties restrict the free rotation around (alkyl)N–P (aryl) bonds, which may cause the generation of more robust active species in higher proportion, leading to extremely high activity along with the generation of a smaller amount of PE.",
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AU - Tahara, Atsushi

AU - Nagashima, Hideo

AU - Lee, Bun Yeoul

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AB - The original Sasol catalytic system for ethylene tetramerization is composed of a Cr source, a PNP ligand, and MAO (methylaluminoxane). The use of expensive MAO in excess has been a critical concern in commercial operation. Many efforts have been made to replace MAO with non-coordinating anions (e.g., [B(C 6 F 5 ) 4 ] − ); however, most of such attempts were unsuccessful. Herein, an extremely active catalytic system that avoids the use of MAO is presented. The successive addition of two equivalent [H(OEt 2 ) 2 ] + [B(C 6 F 5 ) 4 ] − and one equivalent CrCl 3 (THF) 3 to (acac)AlEt 2 and subsequent treatment with a PNP ligand [CH 3 (CH 2 ) 16 ] 2 C(H)N(PPh 2 ) 2 (1) yielded a complex presumably formulated as [1-CrAl (acac)Cl 3 (THF)] 2+ [B(C 6 F 5 ) 4 ] − 2 , which exhibited high activity when combined with iBu 3 Al (1120 kg/g-Cr/h; ~4 times that of the original Sasol system composed of Cr (acac) 3 , iPrN(PPh 2 ) 2 , and MAO). Via the introduction of bulky trialkylsilyl substituents such as –SiMe 3 , –Si(nBu) 3 , or –SiMe 2 (CH 2 ) 7 CH 3 at the para-position of phenyl groups in 1 (i.e., by using [CH 3 (CH 2 ) 16 ] 2 C(H)N[P(C 6 H 4 -p-SiR 3 ) 2 ] 2 instead of 1), the activities were dramatically improved, i.e., tripled (2960–3340 kg/g-Cr/h; more than 10 times that of the original Sasol system). The generation of significantly less PE (<0.2 wt%) even at a high temperature is another advantage achieved by the introduction of bulky trialkylsilyl substituents. NMR studies and DFT calculations suggest that increase of the steric bulkiness on the alkyl-N and P-aryl moieties restrict the free rotation around (alkyl)N–P (aryl) bonds, which may cause the generation of more robust active species in higher proportion, leading to extremely high activity along with the generation of a smaller amount of PE.

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