INORGANIC GRIGNARD ANALOGS - REACTION OF NICKEL POWDER WITH DIHALOGENOTRIORGANOPHOSPHORUS COMPOUNDS TO FORM NICKEL-(II) AND NICKEL-(III) PHOSPHINE COMPLEXES - ISOLATION OF PLANAR [NI(PPH3)I3]- AND THE CRYSTAL-STRUCTURE OF [NI(PPHME2)2BR2]

Reactions of dihalogenotriorganophosphorus compounds R3PX2 (X = Br or I) with unactivated coarse-grain nickel metal powder have been investigated. The nature of the nickel phosphine complexes formed is remarkably dependent on both R and X. Where R not-equal Me and X = I the nickel(II) complexes [R3PI] [Ni(PR3)I3] are formed, analogous to, but not isostructural with, similar cobalt complexes of the same stoichiometry formed from cobalt powder and R3PI2. Quantitative electronic spectroscopic studies indicated that, surprisingly, the [R3PI][Ni(PR3)I3] complexes all have predominantiy square-planar geometry around nickel. Where R = Me and X = 1, the nickel(III) complex [Ni(PMe3)2I3] is obtained in quantitative yield, the other product being diiodine. Reaction of nickel powder with Me2PhPI2 yields both the nickel(II) complex, [MePhPI][Ni(PPhMe2)I3], and the nickel(III) complex, [Ni(PPhMe2)2I3]. These observations again mirror analogous cobalt reactions. Reaction of the analogous dibromo compounds, R3PBr2, with nickel powder is extremely sensitive to the nature of R. Where R = Me, Et or Pn(n) no reaction occurs; where R3 = PhMe2 the square-planar complex [Ni(PPhMe2)2Br2] and an octahedral complex of stoichiometry Ni(PPhMe2)2Br, are obtained in equal yield. Where R3 = Ph2Pr(n) the octahedral complex [Ni(PPh2Prn)2Br4] is formed with a trace of the planar complex [Ni(PPh2Prn)2Br2], and where R = Ph the octahedral complex [Ni(PPh3)2Br4] is formed in quantitative yield. The complex [Ni(PPhMe2)2Br] has been crystallographically characterised: monoclinic, space group P2(1)/a, a = 10.018(2), b = 10.249(1), c = 10.138(1) angstrom and Z = 2 (molecule centrosymmetric).