Co-ordination chemistry of higher oxidation states. Part 4. Palladium(IV) complexes of nitrogen, phosphorus, and arsenic donor ligands. Crystal and molecular structures of [Pd(bipy)Cl4] and [Pd{o-C6H4(AsMe2)2}2Cl2][ClO4]2

Abstract

Octahedral palladium(IV) complexes [Pd(L–L)Cl₄][L–L = Me₂NCH₂CH₂NMe₂, 2,2′-bipyridyl (bipy), 1,10-phenanthroline (phen), Ph₂PCH₂CH₂PPh₂, Me₂PCH₂CH₂PMe₂, Ph₂AsCH₂CH₂AsPh₂, o-C₆H₄(AsMe₂)₂, and Me₂As(CH₂)₃AsMe₂] have been prepared by chlorine oxidation of [Pd(L–L)Cl₂]. The corresponding [Pd(L–L)Br₄][L–L = Me₂PCH₂CH₂PMe₂, o-C₆H₄(AsMe₂)₂, and Me₂As(CH₂)₃AsMe₂] have been obtained, but the [Pd(L–L)Br₂](L–L = N-donors above, Ph₂PCH₂CH₂PPh₂ and Ph₂AsCH₂CH₂AsPh₂) were not oxidised by bromine. The complexes [Pd(L–L)X₄](X = Cl or Br) reductively eliminate X₂ on gentle heating. Chlorine oxidation of Pd(L–L)₂Cl₂ gave Pd(L–L)₂Cl₄ for L–L = Me₂PCH₂CH₂PMe₂ and o-C₆H₄(PMe₂)2, but gave [Pd(L–L)Cl₄] for L–L = Ph₂PCH₂CH₂PPh₂, Ph₂AsCH₂CH₂AsPh₂, and o-C₆H₄(AsMe₂)₂. The complexes trans-[Pd(L–L)₂X₂][ClO₄]₂[X = Cl or Br; L–L = Me₂PCH₂CH₂PMe₂, o-C₆H₄(PMe₂)₂, o-C₆H₄(AsMe₂)₂, or o-C₆H₄(PMe₂)(AsMe₂)] were obtained by HNO₃–HX oxidation of Pd(L–L)₂X₂ followed by addition of HClO₄. Infrared, electronic, and ¹H n.m.r. spectra are reported for the complexes. Attempts to prepare Pdt^IV complexes with multidentate phosphines and arsines are described. The structures of the title compounds have been established by single-crystal X-ray studies. The complex [Pd(bipy)Cl₄] is monoclinic, space group Pn, a= 12.241(5), b= 6.720(2), c= 8.120(9)Å, β= 104.37(5)°, and Z= 2. 1 383 Observed reflections [σ(F)⩽ 2F] refined R to 0.023. The crystal contains discrete octahedral molecules [Pd–Cl 2.289(1)–2.310(1), Pd–N 2.037(4), 2.044(4)Å]. The complex [Pd{o-C₆H₄(AsMe₂)₂}₂Cl₂][ClO₄]₂ is triclinic, space group P, a= 7.903(3), b= 10.670(3), c= 10.141(2)Å, α= 110.50(2), β= 91.75(3), γ= 107.31(3)°, and Z= 1. 1 680 Observed reflections [σ(F)⩽ 3F] refined R to 0.039. The crystal contains trans octahedral cations [Pd–Cl 2.302(2), Pd–As 2.452(1), 2.455(1)] and perchlorate ions [CI–O 1.42(1)Å].