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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