Efficient 1-hexene trimerization with triazacyclohexane chromium catalysts and detailed product analysis by 13C NMR

Alexander G. N Coxon, Randolf D. Kohn

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Abstract

Triazacyclohexane chromium precatalysts are described which catalyze the selective trimerization of 1-pentene, 1-hexene, and 1-octene with unprecedented activity, reaching nearly 5000 turnovers in 1 h. The isomer distribution of the trimers has been analyzed in detail by application of quantitative 13C NMR spectroscopy to 13C labeled samples. All endocyclic elimination products predicted by the metallacyclic mechanism have been characterized, and many have been confirmed by their independent syntheses. Significant variations in the isomer distribution are observed on variation of the ligand bulk. Quantification gave considerable insights into the relative abundance of metallacyclic intermediates, with 1,3-substituted chromacyclopentanes being by far the most abundant resting state. Ring expansion selectivity favors 1,2-insertion into the less hindered Cr–C bond, but some 2,1-insertion products have also been identified.
Original languageEnglish
Pages (from-to)3008-3016
Number of pages9
JournalACS Catalysis
Volume6
Issue number5
Early online date30 Mar 2016
DOIs
Publication statusPublished - 6 May 2016

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Keywords

  • selective olefin trimerization
  • catalysis
  • chromium
  • 13C NMR characterization
  • metallacycle
  • oligomerization

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