The present invention relates to olefin polymerization catalysts including a novel phenoxyaminetitanium(II) alkene complex, rac-Lig2 TiBn, which is inactive for olefin polymerization upon benzyl abstraction, treatment with ethylene leads to the formation of a stable titanacyclopentane complex (rac-Lig2(CH2)2TiBn). Six-membered metallacycle complexes (rac-Lig1ZrBn2-a,b and rac-Lig1HfBn2-a,b) were obtained from reaction of the vinylappended ligand with tetrabenzylzirconium (ZrBn4) or tetrabenzylhafnium (HfBn4). Living and isoselective polymerization of 1-hexene was promoted by rac-Lig1HfBn2- a,b/B(C6F5)3 at 0°C, while rac-Lig1ZrBn2-a,b/B(C6F5)3 catalyzed the living and isoselective polymerization of propylene at 0°C. This catalyst system was employed for the synthesis of a diblock copolymer featuring an isotactic polypropylene semicrystalline block and poly(ethylene-co-propylene) amorphous block. Complexes derived from rac-Lig1HfBn2-a,b and rac-Lig1ZrBn2-a,b also served as highly active cyclopolymerization catalysts for 1,5- hexadiene which furnished poly(methylene-l,3-cyclopentane) with a predominance of cis- cyclopentane rings. Lastly, cyclopolymerization of 1,6-heptadiene with rac-Lig1HfBn2- a,b/B(C6F5)3 produced poly(methylene-1,3-cyclohexane) with a nearly perfect cis-isotactic microstructure.