A bisphosphonite calix[5]arene ligand that stabilizes η6 arene coordination to palladium

Treatment of a bis(phenylphosphonite)calix[5]arene ligand with either palladium(II) chloride or 1,5-cyclooctadieneplatinum(II) chloride yields square planar metal complexes in which the two phosphorus atoms bind cis to the MCl(2) moiety (M = Pd, Pt). Chloride was removed from the palladium complex to open a coordination site at the metal for catalysis. The chloride removal resulted in a rare and unexpected η(6) coordination of an arene to the metal. The reaction is reversible upon addition of tetra-n-butyl ammonium chloride.