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

Abstract

Displacement of ethene from [Pt(η²-C₂H₄)(dcpe)] by Ph₂PCCMe gives the monomeric η²-alkynylphosphine complex [Pt(η²-Ph₂PCCMe)(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)CCMe)(dcpe)] (X = S (9), O (10)). Complexes 5, 6, 8, 9 and 10 have been structurally characterised by single-crystal X-ray diffraction analysis.