CpTiCl2(NCtBu2) exhibits both remarkable catalytic activity and efficient norbornene (NBE) incorporation for ethylene–NBE copolymerization: the NBE incorporation by Cp′TiCl2(X) (X = NCtBu2, O-2,6-iPr2C6H3; Cp′ = Cp, C5Me5, indenyl) was related to the calculated coordination energy after ethylene insertion.