The mechanistic differences between tri- and tetramerization of ethane have recently been gaining interest in order to find new catalytic systems.

Uwe Rosenthal and co-workers, Rostock University, Germany, have studied the coordination, deprotonation, rearrangement, and cleavage of the ethene trimerization ligand Ph₂PN(iPr)P(Ph)N(iPr)H by trialkylaluminium compounds.

With increasing temperature and residence time the reaction sequence from Ph₂PN(iPr)P(Ph)N(iPr)H via the adduct [Ph₂PN(iPr)P(Ph)N(iPr)H][AlR₃], the aluminium amide [Ph₂PN(iPr)P(Ph)(AlR₃)N(iPr)][AlR₂], the rearranged cyclic compound [N(iPr)P(Ph)P(Ph₂)N(iPr)][AlR₂], and finally the cleaved cyclic dimer [R₂AlN(iPr)P(Ph)₂]₂ is observed.

The system consists of the trimerization ligand, CrCl₃(THF)₃, and Et₃Al; this produces 1-hexene in more than 90 % yield with high purity and provides vital information for activation and deactivation mechanisms.

• Activation and Deactivation by Temperature: Behavior of Ph₂PN(iPr)P(Ph)N(iPr)H in the Presence of Alkylaluminum Compounds Relevant to Catalytic Selective Ethene Trimerization
  S. Peitz, N. Peulecke, B. R. Aluri, B. H. Müller, A. Spannenberg et al.,
  Chem. Eur. J. 2010, 16(40).
  DOI: 10.1002/chem.201001936