A new series of catalysts for ethylene and ethylene/1-hexene (co)polymerizations bearing constrained hydroxyindanone-imine ligands was developed for titanium(IV) and zirconium(IV) metals with variations of steric and electronic contributions on the ligands. X-ray crystal structures revealed significantly higher open space for the constrained titanium and zirconium complexes, compared to the conventional FI counterparts. Upon activation with MAO, significantly higher ethylene polymerization activities (up to 379.4 kg-PE/mmol-M h for Zr) and notably almost doubled 1-hexene content in the ethylene/1-hexene copolymerizations were observed as a result of the constrained five-membered ring backbone.