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 MX 2 (M = Zr or Hf, X = NMe 2, Cl, or Me) and MX 2 (M = Zr or Hf, X = NMe 2, Cl, Me). The structures of ZrMe 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 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 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.