Preparation, characterization and activity of palladium(II) halide complexes with diethyl 2-quinolylmethylphosphonate (2-dqmp). X-Ray crystal structures of trans-[Pd(2-dqmp)2X2](X = Cl or Br)

Abstract

A series of new palladium(II) halide complexes with diethyl 2-quinolylmethylphosphonate (2-dqmp) were prepared and studied. Two types of square-planar palladium dihalide complexes, trans-[Pd(2-dqmp)₂X₂] with the N-bonded monodentate ligand and cis-[Pd(2-dqmp)X₂] where dqmp acts as a bidentate N,O-bonded chelate ligand, could be obtained by reaction of 2-dqmp with [PdX₄]^2–(X = Cl or Br) in neutral methanolic-aqueous solution. The ion-pair salt complexes, [2-Hdqmp]₂[PdX₄], containing the protonated quinoline ligand as cation and the square-planar tetrahalogenopalladate complex as anion, were isolated upon treatement of the ethanolic–aqueous solution with HX. The new complexes were identified and characterized by elemental and thermogravimetric analysis, magnetic and conductometric measurements, and by infrared and ¹H NMR spectral studies. All were tested for cytostatic activity on KB and L1210 cell lines, but only [Pd(2-dqmp)₂Br₂]2 displayed a significant anti-tumour effect in both systems. The molecular structures of the complexes [Pd(2-dqmp)₂X₂](X = Cl, 1; Br, 2) were determined by single-crystal X-ray analysis. The crystals are triclinic, space group P, Z= 2, with other parameters: 1, a= 10.209(3), b= 9.812(3), c= 8.949(2)Å, α= 78.36(2), β= 94.82(2), γ= 111.60(2)°, R= 0.0598, and R′= 0.0648 for 2982 observed reflections; 2, a= 10.502(3), b= 9.405(3), c= 9.009(3)Å, α= 72.00(2), β= 103.96(2), γ= 100.63(2)°, R= 0.0574, and R′= 0.0614 for 2033 observed reflections. Each complex has a trans square-planar structure, the palladium being co-ordinated by two halogen and two nitrogen atoms and lying at a centre of symmetry.