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

A range of triazacyclohexane (R3TAC) complexes of CrCl3 with unsaturated N-substituents R have been prepared. Addition of HX or X2 (X = Cl or Br) across the double bonds of the complexed ligand gives access to N-substituents containing halogen atoms. The halogenated catalysts give non-halogenated analogues in ethylene polymerization and trimerisation when activated with MAO lending support to the concept of some positive “halogen effect” on the catalysis.