Olefin polymerizations catalyzed by Cp'TiCl2(0-2,6-(Pr2C6H3)-Pr-i) (1-5; Cp' = cyclopentadienyl group), RuCl2(ethylene)(pybox) {7; pybox = 2,6-bis[(4S)-4-isopropyl-2-oxazolin-2-yl] pyridine}, and FeCl2(pyhox) (8) were investigated in the presence of a cocatalyst. The Cp*TiCl2(0-2,6-Pr,C,H,) (5)-methylaluminoxane (MAO) catalyst exhibited remarkable catalytic activity for both ethylene and l-hexene polymerizations, and the effect of the substituents on the cyclopentadienyl group was an important factor for the catalytic activity. A high level of 1-hexene incorporation and a lower r(E) . r(H) value with 5 than with [Me2Si(C5Me,)((NBu)-Bu-t)]TiCl2 (6) were obtained, despite the rather wide bond angle of Cp-Ti-O (120.5 degrees) of 5 compared with the bond angle of Cp-Ti-N of 6 (107.6 degrees). The 7-MAO catalyst exhibited moderate catalytic activity for ethylene homopolymerization and ethylene/1-hexene copolymerization, and the resultant copolymer incorporated 1-hexene. The 8-MAO catalyst also exhibited activity for ethylene polymerization, and an attempted ethylene/1-hexene copolymerization gave linear polyethylene. The efficient polymerization of a norbornene macromonomer bearing a ring-opened poly(norbornene) substituent was accomplished by ring-opening metathesis polymerization with the well-defined Mo(CHCMe2Ph)(N-2,6-(Pr2C6H3)-Pr-1) [OCMe(CF,),], (10). The key step for the macromonomer synthesis was the exclusive end-capping of the ring-opened poly(norbornene) with p-Me3SiOC6H4CHO, and the use of 10 was effective for this polymerization proceeding with complete conversion.