Synthesis, Characterization, and Polymerization Behavior of Zirconium and Hafnium Complexes that Contain Asymmetric Diamido-N-Donor Ligands

Two new “NNN” (diamido-N-donor) ligands have been synthesized that contain ethylene/ o -phenylene “arms” and a phenyl-substituted amine donor in the central position, [MesitylNH- o -C 6 H 4 N(Ph)CH 2 CH 2 NHMesityl] (H 2 1 ) and [ t -Bu d6 -NH- o -C 6 H 4 N(Ph)CH 2 CH 2 NHMesityl] (H 2 2 ). 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 6 H 4 NCH 2 CH 2 NMesityl]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 3 C][B(C 6 F 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.