Novel octahedral zirconium complexes bearing alkoxide functionalized N-heterocyclic carbene ligands have been synthesized and characterized. NMR analysis showed that more than one species was obtained during synthesis. The synthesized complexes were able to polymerize ethylene and propylene giving rise to a linear polyethylene with high Mw and polydispersity index often bimodal with molecular weight distribution (MDI) > 2, and highly isotactic polypropylene together with an atactic fraction. Density functional theory (DFT) studies on the complex stability indicate the possible species active during the polymerization reaction. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012