Isotopic labelling in ethylene oligomerization: addressing the issue of 1-octene vs. 1-hexene selectivity.

The selectivity-determining mechanistic steps of ethylene tetramerization and trimerization are evaluated in light of isotopic labeling experiments. A mechanism based upon a shared chromacycloheptane intermediate rather than the C-C coupling of chromacyclopentanes or Cr speciation into independent trimerization and tetramerization catalysts is consistent with the data, including observed upper limits on 1-octene selectivity.