Co-ordination chemistry of higher oxidation states. Part 8. Nickel(III) complexes of bi- and multi-dentate phosphorus and arsenic ligands; crystal and molecular structure of [Ni(Ph2PCH2CH2PPh2)Br3]·C6H5Me

Abstract

The five-co-ordinate nickel(III) complexes [Ni(L–L)Cl₃][L–L = Ph₂PCH₂CH₂PPh₂, Ph₂P(CH₂)₃PPh₂, Ph₂PCHCHPPh₂, o-C₆H₄(PPh₂)₂, or Me₂PCH₂CH₂PMe₂] have been obtained by Cl₂ or NOCl oxidation of [Ni(L–L)Cl₂] in CCl₄ or CH₂Cl₂. The bromides [Ni(L–L)Br₃][L–L = as above, o-C₆H₄(AsPh₂)₂, or o-C₆H₄(PPh₂)(SMe)] are obtained similarly using Br₂–CCl₄. On gentle heating, [Ni(L–L)X₃](X = Cl or Br) lose X₂ to reform [Ni(L–L)X₂]. Unstable [Ni{o-C₆H₄(AsMe₂)₂}X₃] have been prepared by halogenation of the dicarbonyl [Ni(CO)₂{o-C₆H₄(AsMe₂)₂}]. The complexes have been characterised by i.r., electronic, and e.s.r. spectroscopy, and by magnetic measurements, and the structure of [Ni(Ph₂PCH₂CH₂PPh₂)Br₃]·C₆H₅Me established by a single-crystal X-ray study. It is monoclinic, space group P2₁/n, and has a= 15.567(3), b= 14.627(2), c= 15.151(3)Å, β= 113.38(2)°, and Z= 4. The structure was refined to R= 0.0562 from 1 583 reflections. The five-co-ordinate nickel is in an approximately square-pyramidal arrangement [Ni–Br 2.346(3), 2.417(3), and 2.363(3); Ni–P 2.223(5) and 2.236(5)Å], and lies above the P₂Br₂ plane toward the apical bromine. The synthesis and properties of pseudo-octahedral [Ni(L′–L′)₂X₂]Y [L′–L′=o-C₆H₄(PMe₂)₂, o-C₆H₄(AsMe₂)(PMe₂), o-C₆H₄(PMe₂)(SbMe₂), or Me₂P(CH₂)₂PMe₂; X = Cl or Br; Y = BF₄ or ClO₄] are described. The compounds mer-[Ni{PhP(CH₂CH₂PPh₂)₂}X₃] have also been obtained, but attempts to prepare nickel(III) complexes with quadridentate phosphines were unsuccessful.