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.
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