Coordination Chemistry of Large Diphosphanes − Directional Properties of a Calix[4]arene Proximally Substituted by Two −OCH 2 PPh 2 Podand Arms

The proximally‐functionalised calixarene 5,11,17,23‐tetra‐ tert ‐butyl‐25,26‐bis(diphenylphosphanylmethoxy)‐27,28‐dihydroxycalix[4]arene ( 1 ), a large diphosphane in which the P III centres are separated by 10 bonds, behaves as a chelating ligand towards NiX 2 moieties (X = Cl, Br). As shown by three X‐ray studies carried out on complexes of the type [NiX 2 ·1 ], the diphosphane is able to accommodate either tetrahedral or strongly distorted tetrahedral coordination geometries, but not a square planar one. In all structures, the ligand positions the nickel atom away from the calixarene axis. In the presence of methylaluminoxane (MAO), [NiCl 2 ·1 ] effectively catalyses the oligomerisation of ethylene, affording C 4 −C 12 oligomers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)