Preparation and characterization of nickel(II), palladium(II), and platinum(II) complexes containing (2-aminoethyl)dimethylphosphine or the related didentate phosphine ligands

Article abstract of DOI:10.1246/bcsj.69.2539

Here are described several new nickel(II), palladium(II), and platinum(II) complexes of bis(chelate)-type with didentate phosphine ligands having an amino or thioether donor group: Me₂PCH₂CH₂NH₂ (edmp), Ph₂PCH₂CH₂NH₂ (edpp), Me₂PCH₂CH₂NMe₂ (dmedmp), or Me₂PCH₂CH₂SMe (mtdmp). Bis(tetrafluoroborate) salts of [M(P-N or S)₂]²⁺ (M=Ni, Pd, and Pt; (P-N or S)=the ligands above) have been prepared and the geometrical structures determined by NMR spectroscopy. All the palladium(II) complexes prepared in this study are cis-isomers, in contrast to the analogous Me₂PCH₂CH₂S^- (dmsp) complex (trans-[Pd(dmsp)₂]), which indicates that the anionic phosphine-thiolate ligand prefers the trans geometry more than the neutral phosphine-amine or -thioether ligand does. The dichloride salts of the bis(edmp) complexes, cis-[M(edmp)₂]Cl₂ (M=Ni (4a), Pd(5a), and Pt(6a)), and those of the bis(edpp) complexes have been obtained as crystals, while the corresponding salts of dmedmp, mtdmp, and 8-(dimethylphosphino)quinoline complexes can not be isolated due to their oily properties. Further, addition of LiBF⁴ to a methanolic solution of 4a, 5a, or 6a gives exclusively a precipitate of the chloride tetrafluoroborate salt, cis-[M(edmp)₂]Cl(BF₄) (M=Ni (4c), Pd(5c), or Pt(6c)). The crystal structures of 4a, 5c, and 6a determined by X-ray analyses indicate a weak (not strong enough to form a five-coordinated complex) interaction between cis-[M(edmp)₂]²⁺ and Cl^- anion. The average M-N bond lengths in 4a, 5c, and 6a are considerably longer than those in the corresponding 1,2-ethanediamine complexes, owing to the strong trans influence of the -PMe₂ group in edmp. The order of strength of the trans influence among Ni^II, Pd^II, and Pt^II triad metal series is nonperiodical: Ni^II < Pt^II < Pd^II. This order is similar to the order among Co^III, Rh^III, and Ir^III triad metal series found in our previous study on fac-[M′(edmp)₃]³⁺ (M′ =Co^III, Rh^III, and Ir^III) complexes.