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

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 C6H4But-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.

Graphical abstractChiral and achiral p-tert-butyl-calix[4]arene bisphosphites and their Pd and Pt complexes are reported. The crystal lattices of PdCl2 complexes of chiral bisphosphites display hydrophobic channels and the molecules are held together by intermolecular C–H⋯Cl hydrogen bonds.Figure optionsDownload full-size imageDownload as PowerPoint slide