Selective trimerisation and polymerisation of ethylene: Halogenated chromium triazacyclohexane complexes as probes for an internal 'halogen effect'

Randolf Kohn, Alexander G N Coxon, Christopher R. Hawkins, David Smith, Shahram Mihan, Katrin Schuhen, Michael Schiendorfer, Gabriele Kociok-Köhn

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Abstract

A range of triazacyclohexane (R3TAC) complexes of CrCl3 with unsaturated N-substituents R have been prepared. The complexes with R = allyl (3f) and CH2CH(CH2CH = CH2)2 (3h) have been characterised by X-ray crystallography. Addition of HX or X2 (X = Cl or Br) across the double bonds of the complexed ligand gives access to β- and γ-branched N-substituents containing three to twelve organic halogen atoms. The complexes with R = CH2CHBrCH2Br (3k), CH2CH2CX(nC5H11)2 (X = Cl (3n) and Br (3o)) have been characterised by X-ray crystallography. N-substituent chlorinated complexes can also be prepared via alkyl chloride containing amines as demonstrated for a crystal structure of a complex with R = (CH2)3Cl (3e). Complexes with β-branched N-substituents give high selectivity for ethylene trimerisation to 1-hexene while complexes with γ-branched N-substituents are good ethylene polymerisation catalysts. The halogenated polymerisation catalysts give higher activities than their hydrogenated analogues, especially chlorine containing species. Chlorinated trimerisation catalysts demonstrated significantly improved 1-hexene selectivities, though activity was similar to hydrogenated alternatives. This lends support to the concept of a positive 'halogen effect' on the catalysis.

Original languageEnglish
Pages (from-to)3-13
Number of pages11
JournalPolyhedron
Volume84
Early online date5 Jun 2014
DOIs
Publication statusPublished - 14 Dec 2014

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Halogens
Chromium
halogens
chromium
Ethylene
ethylene
polymerization
X ray crystallography
Polymerization
methylidyne
Catalysts
probes
Catalyst selectivity
Chlorine
Catalysis
Amines
Chlorides
Catalyst activity
hexenes
Crystal structure

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Selective trimerisation and polymerisation of ethylene : Halogenated chromium triazacyclohexane complexes as probes for an internal 'halogen effect' . / Kohn, Randolf; Coxon, Alexander G N; Hawkins, Christopher R.; Smith, David; Mihan, Shahram; Schuhen, Katrin; Schiendorfer, Michael; Kociok-Köhn, Gabriele.

In: Polyhedron, Vol. 84, 14.12.2014, p. 3-13.

Research output: Contribution to journalArticle

Kohn, Randolf ; Coxon, Alexander G N ; Hawkins, Christopher R. ; Smith, David ; Mihan, Shahram ; Schuhen, Katrin ; Schiendorfer, Michael ; Kociok-Köhn, Gabriele. / Selective trimerisation and polymerisation of ethylene : Halogenated chromium triazacyclohexane complexes as probes for an internal 'halogen effect' . In: Polyhedron. 2014 ; Vol. 84. pp. 3-13.
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abstract = "A range of triazacyclohexane (R3TAC) complexes of CrCl3 with unsaturated N-substituents R have been prepared. The complexes with R = allyl (3f) and CH2CH(CH2CH = CH2)2 (3h) have been characterised by X-ray crystallography. Addition of HX or X2 (X = Cl or Br) across the double bonds of the complexed ligand gives access to β- and γ-branched N-substituents containing three to twelve organic halogen atoms. The complexes with R = CH2CHBrCH2Br (3k), CH2CH2CX(nC5H11)2 (X = Cl (3n) and Br (3o)) have been characterised by X-ray crystallography. N-substituent chlorinated complexes can also be prepared via alkyl chloride containing amines as demonstrated for a crystal structure of a complex with R = (CH2)3Cl (3e). Complexes with β-branched N-substituents give high selectivity for ethylene trimerisation to 1-hexene while complexes with γ-branched N-substituents are good ethylene polymerisation catalysts. The halogenated polymerisation catalysts give higher activities than their hydrogenated analogues, especially chlorine containing species. Chlorinated trimerisation catalysts demonstrated significantly improved 1-hexene selectivities, though activity was similar to hydrogenated alternatives. This lends support to the concept of a positive 'halogen effect' on the catalysis.",
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AU - Coxon, Alexander G N

AU - Hawkins, Christopher R.

AU - Smith, David

AU - Mihan, Shahram

AU - Schuhen, Katrin

AU - Schiendorfer, Michael

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