The coordination chemistry of simple phospholes: Complexes of nickel(II), palladium(II) and platinum(II)

The reactions between four very simply substituted phospholes and the chlorides of Ni(II), Pd(II) and Pt(II) are described. The phospholes 1-phenylphosphole, 3-methyl-1-phenyl-phosphole and 3,4dimethyl-1-phenylphosphole all readily form bis-complexes of formula L₂MCl₂ L = phosphole ligand and M = Ni(II), Pd(II) or Pt(II)] or tris-complexes of formula L₃MCI₂. 1-n-Butyl-3,4-dimethylphosphole appears to form stable complexes only with Ni(II). Evidence is put forward which indicates that the L₂MCl₂ complexes exist in a four-coordinate, square-planar monomeric/five coordinate equilibrium while the L₃MCl₂ complexes are primarily the ionic species L₃MCl]⁺ Cl^? in solution. Comparisons are made with the behaviour of other simple phospholes which do not form Ni(II) complexes and the results are discussed briefly in terms of both aromatic and non-aromatic phosphole models.