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

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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.

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