Inorganic grignard analogues. Reaction of nickel powder with dihalogenotriorganophosphorus compounds to form nickel-(II) and -(III) phosphine complexes; isolation of planar [Ni(PPh3)I3]– and the crystal structure of [Ni(PPhMe2)2Br2]

Abstract

Reactions of dihalogenotriorganophosphorus compounds R₃PX₂(X = Br or I) with unactivated coarsegrain nickel metal powder have been investigated. The nature of the nickel phosphine complexes formed is remarkably dependent on both R and X. Where R ≠ 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 predominantly square-planar geometry around nickel. Where R = Me and X = I, the nickel(III) complex [Ni(PMe₃)₂I₃] is obtained in quantitative yield, the other product being diiodine. Reaction of nickel powder with Me₂PhPl₂ yields both the nickel(II) complex, [Me₂PhPI][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 Pnⁿ no reaction occurs; where R₃= PhMe₂ the square-planar complex [Ni(PPhMe₂)₂Br₂] and an octahedral complex of stoichiometry Ni(PPhMe₂)₂Br₄ are obtained in equal yield. Where R₃= Ph₂Prⁿ 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)₂Br₂] has been crystallographically characterised: monoclinic, space group P2₁/a, a= 10.018(2), b= 10.249(1), c= 10.138(1)Å and Z= 2 (molecule centrosymmetric).