Strained Diphosphines Built upon a Calix[4]arene Skeleton. Synthesis of a Highly Active Norbornene Polymerization Catalyst

Summary: The complexes cis‐P,P′‐(η⁵‐cylopentadienyl)‐{5,17‐dibromo‐11,23‐bis(diphenylphosphino)‐25,26,27,28‐tetrapropoxy‐calix[4]arene}nickel(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 diphosphine, 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 × 10⁵ 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.

Molecular structure of 2 .