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

Polyhedron, ISSN: 0277-5387, Vol: 84, Page: 3-13
2014
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Article Description

A range of triazacyclohexane (R 3 TAC) complexes of CrCl 3 with unsaturated N-substituents R have been prepared. The complexes with R = allyl ( 3f ) and CH 2 CH(CH 2 CH = CH 2 ) 2 ( 3h ) have been characterised by X-ray crystallography. Addition of HX or X 2 (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 = CH 2 CHBrCH 2 Br ( 3k ), CH 2 CH 2 CX( n C 5 H 11 ) 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 = (CH 2 ) 3 Cl ( 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.

Bibliographic Details

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

Elsevier BV

Chemistry; Materials Science

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