The complexes cis-P,P'-(eta(5)-cylopentadienyl)-{5, 17-dibromo-11, 23-bis(diphenylphosphino)-25,26,27,28-tetrapropoxy-calix[4]arene}nickle( II) tetrafluoroborate (1) and dibromo-{5, 17-dibromo-11 23-bis(diphenylphosphino)-25,26,27,28-tetrapropoxycalix[4]arene}nickel(II) (2), both of which contain a constrained chelating disphosphine, were evaluated for the polymerization of norbornene. Combined with methylaluminoxane, they result in remarkably, active systems for the production of high-molar-mass vinyl-type polynorbornene. Turnover frequencies of up to 7.5 x 10(5) mol(NBE) . mol(Ni)(-1) . h(-1) are observed. A plausible explanation for their high performances relies on a periodic P-Ni-P bite angle enlargement that temporarily increases the steric hindrance about the catalytic centre, which in turn favours the insertion steps.