Synthesis, characterization, and polymerization behavior of zirconium and hafnium complexes that contain asymmetric diamido-N-donor ligands

Two new "NNN" (diamido-N-donor) luiganda have been synthesized that contain ethylene/ o-phenylene "arms" and a phenyl-substituted amine donor in the central position, [Mesityl-NH-o-C ₆H ₄N(Ph)CH ₂CH ₂NHMesityl] (H ₂1) and [t-Bu _d6-NH-o-C ₆H ₄N(Ph)CH ₂CH ₂NHMesityl] (H ₂1). The Zr and Hf complexes that have been isolated include [1]MX ₂ (M = Zr or Hf, X = NMe ₂, Cl, or Me) and [2]MX ₂ (M = Zr or Hf, X = NMe ₂, Cl, Me). The structures of [1]ZrMe ₂, [2]ZrMe ₂, and a dimeric species with the formula [MesitylN-o-C ₆H ₄NCH ₂CH ₂NMesityl]Zr ₂-(NMe ₂) ₅ have been determined in X-ray crystallographic studies. Abstraction of a methyl group in [1]MMe ₂ (M = Zr or Hf) with [Ph ₃C] [B(C ₆F ₅) ₄] gives rise to cationic complexes that are active initiators for the polymerization of 1-hexene. Similar activation of [2]MMe ₂ (M = Zr or Hf) gives rise to dimeric monocations that eventually break up and react further to yield cationic monomethyl species. In all cases the poly[1-hexene] produced in the presence of the monometallic cations was found to be atactic.