Evidence for platinum(II)-vinylidene complexes and their reactions with water to give hydrocarbons and olefins

Treatment of the alkynyl complexes trans-[Pt(Me)(CCR)(PPh3)2] (R=p-tolyl (1a), Ph (1b)) at low temperature in a CD2Cl2 solution with stoichiometric amounts of the acids HBF4·Et2O or CF3SO3H affords the corresponding vinylidene derivatives trans-[Pt(Me){=C=C(H)R}(PPh3)2]X (R=p-tolyl, X=BF4 (2aBF4); R=p-tolyl, X=CF3SO3 (2aCF3SO3); R=Ph, X=BF4 (2bBF4)) on the basis of 1H- and 31P{1H}-NMR data. The reactions of the in situ generated complexes 2 with water, which were followed by 1H- and 31P{1H}-NMR, lead to the formation of a mixture of the carbonyl complex [Pt(Me)(CO)(PPh3)2]X (3) and the hydroxo-bridged dinuclear compound [Pt(μ-OH)(PPh3)2]2X2 (4) in a ca. 1:2 ratio. The formation of 3 and 4 is accompanied with the liberation of hydrocarbons R-CH3 and olefins CH3CH=CHR (R=p-tolyl, Ph), respectively, which arise from the vinylidene ligand likely via an hydroxycarbene intermediate