New zirconium complexes bearing indolyl-pyridylamido ligands [-NNN-] have been synthesized and used as catalysts in ethylene and propene polymn. in the presence of AliBu2H/MAO as cocatalytic system. Complexes 1 and 2, bearing ligands with a different steric hindrance on the carbon bridging the pyridine and the aniline moieties, exhibited remarkable catalytic activity for ethylene and propene polymn., affording ultrahigh mol. wt. polymers with monomodal mol. wt. distributions. Moreover, the presence of the 2-iso-Pr Ph substituent on the bridging carbon (complex 2) resulted in higher stereoselectivity and regioselectivity providing a polypropylene sample with an [mmmm] content up to 96% and 1.3% of regioinversion. On the other hand, the change of the substituents of the aniline moiety (complex 3) gave a zirconium complex which resulted completely inactive both in the ethylene and propene polymn.