The synthesis and spectroscopic properties (¹H and ³¹P n.m.r., i.r.) of complexes containing the β-ketophosphine Ph₂PCH₂C(O)Ph (HL) are described. In [NiX₂(HL)₂][X = Cl (1), Br, or I (3)], [PdCl₂(HL)₂](4), [PtCl₂(HL)₂](5), and [{PdCl(µ-Cl)(HL)}₂](6), HL behaves as a P-bonded monodentate ligand whereas in the cationic complexes [Pd(HL)₂][BF₄]₂ and [{Pd(µ-Cl)(HL)}₂][CF₃SO₃]₂ it acts as a P,O chelate. The crystal structures of (1) and (3) have been determined using single-crystal X-ray diffraction methods. Compounds (1) crystallises in space group P2₁/n, with a= 10.079(3), b= 11.510(3), c= 15.411(3)Å, β= 93.42(2)°, and Z= 2. Compound (3) crystallises in space group P2₁/c, with a= 9.283(1), b= 10.261(1), c= 19.318(1)Å, β= 96.20(1)°, and Z= 2. The structures have been refined to R 0.050 (R′ 0.060) for (1) and to R 0.032 (R′ 0.041) for (3). The geometries of these complexes are essentially identical although the ν(CO) frequencies of these complexes are significantly different [1 662 cm^–1 for (1) and 1 620 cm^–1 for (3)]; the nickel atom occupies a centre of symmetry and has thus a square-planar environment. Although the ketone group is bent towards the nickel atom, no significant Ni–O bonding interaction occurs, as deduced from the Ni–O distances [3.230(4)Å in (1) and 3.231(1)Å in (3)]. In refluxing toluene (1), (4), or (5) lead to the phosphine–phosphinite complexes cis-[[graphic omitted]Ph₂}](M = Ni, Pd, or Pt). Treatment of (1), (4), or (5) with base gives the enolato-complexes cis-[[graphic omitted]Ph}₂](M = Ni, Pd, or Pt). Reaction of (6) with NaH affords the binuclear complex [{P[graphic omitted]Ph]}₂]. The latter reacts with PPh₃ to give cis-[P[graphic omitted]Ph}(PPh₃)], and with Ph₂PCH₂CH₂PPh₂–TlPF₆ to give [P[graphic omitted]Ph}(Ph₂PCH₂CH₂PPh₂)]PF₆. The P–O coupling products [N[graphic omitted]R}](R = Cl or Ph) are obtained by reaction of the complex [N[graphic omitted]Ph}₂] with PCl₃ and PPhCl₂ respectively, and shown to have a five-co-ordinate structure. The square-planar P,P,P complex [N[graphic omitted]Ph}]PF₆ results from reaction of [N[graphic omitted]Ph}] with TIPF₆.