New stable aryl-substituted acyclic imino-N-heterocyclic carbene: Synthesis, characterisation and coordination to early transition metals

The synthesis of the bulky 1-(1-arylimino-2,2-dimethylpropyl)-3-(aryl) imidazolium salt from the corresponding imidazole and the activated imidoyl chloride is presented. The absence of acidic protons adjacent to the iminic carbon allowed for the first isolation of an imino-N-heterocyclic carbene of this ligand class. The free carbene was isolated, structurally characterised, and coordinated to titanium, zirconium, hafnium and chromium. The resulting metal halide complexes were fully characterised and were tested at room temperature and atmospheric pressure for their activity as ethylene polymerisation catalysts. The Zr(iv) complex was found to be the most active with a productivity of 140 kg PE mol M^-1 h^-1.