Palladium and platinum complexes of chiral and achiral calix[4]arene bisphosphite ligands

Abstract

Chiral and achiral p-tert-butyl-calix[4]arene bisphosphites (L¹-L³) have been synthesized by the reaction of p-tert-butyl-calix[4]arene and the phosphorodichloridites, ROPCl₂ [R = (1S,2R,5R)-(+)-iso-menthyl (L¹), (1R,2S,5R)-(-)-menthyl (L²) or C₆H₄Bu^t-4 (L³)]. These bisphosphites function as chelating ligands in palladium(II) and platinum(II) complexes which are formed in good yields by the reaction of PdCl₂(PhCN)₂, MCl₂(COD) (M = Pd or Pt) or PdMeCl(COD) with the respective calix[4]arene bisphosphite. Single crystal X-ray diffraction studies performed on the complexes [PdCl₂(L¹)], [PdCl₂(L²)], [PdCl₂(L³)] and [PtCl₂(L³)] reveal a near square planar geometry around the metal with the two chloride ligands in a cis disposition. The crystal packing in the complexes [PdCl₂(L¹)] and [PdCl₂(L²)], which crystallize in the chiral (P6₁22) space group, shows different hydrophobic channels with intermolecular C-H···Cl hydrogen bonding. The complexes [PdCl₂(L³)] and [PtCl₂(L³)] are isostructural and the molecules in the crystal lattice are linked by intermolecular C-H···Cl and C-H···O hydrogen bonds.