Preparation and reactivity of mononuclear platinum(0) complexes containing a η²-coordinated alkynylphosphine

Displacement of ethene from [Pt(η²-C₂H₄)(dcpe)] by Ph₂PC≡CMe gives the monomeric η²-alkynylphosphine complex [Pt(η²-Ph₂PC≡CMe)(dcpe)] (5). Reaction of 5 with one equivalent of HCl forms, in benzene, the four-coordinate η¹-vinyl-platinum(II) complex [PtCl{C(=CHMe)PPh₂}(dcpe)] (6) by regiospecific addition of the proton to the alkyne carbon atom bearing the methyl group. In dichloromethane, reversible dissociation of the chloride ion from 6 takes place and the cation [Pt{C(=CHMe)PPh₂-κP,C¹}(dcpe)]⁺ (6′) that contains a three-membered methylenephosphaplatinacycle fragment can be observed. Treatment of complex 5 with methyl iodide results in the formation of a phosphonium salt [Pt{η²-C(=CH₂)=CHPPh₂Me}(dcpe)] ⁺I^-, [8]I, in which the alkynylphosphine has rearranged to the corresponding allene. The alkynylphosphine complex 5 is cleanly oxidised at phosphorus in the presence of sulfur or air to give the corresponding sulfide or oxide [Pt(η²-Ph₂P(X)C≡CMe)(dcpe)] (X = S (9), O (10)). Complexes 5, 6, 8, 9 and 10 have been structurally characterised by single-crystal X-ray diffraction analysis.