Cavitand Chemistry: Nickel Half‐Sandwich Complexes with Imidazolylidene Ligands Bearing One or Two Resorcinarenyl Substituents

Two imidazolium salts, one with a single N ‐µ 4 ‐tetramethylenedioxyresorcin[4]arenyl substituent, the other with two, have been used as pro‐ligands (LH) for the synthesis of nickel half‐sandwich complexes of the type [NiCpClL] (Cp = cyclopentadienyl). NMR and X‐ray structural investigations revealed that in both complexes the NiCp moiety is positioned at the wider entrance of the resorcinarenyl cavity, this location providing high steric encumbrance around the metal centre. Both complexes, once activated with NaBH 4 , catalysed the dimerisation of ethylene, the highest activity [555 mol(C 2 H 4 ) mol(Ni) –1 h –1 ] being observed with the complex bearing two cavitand substituents.