The novel ?-phosphorus labile ylide of 1-(p-tolyl)-2-(tri-p-tolylphosphoranylidene)ethanone (PTTPPY) is prepared by the reaction of 2-bromo-1-(p-tolyl)ethanone with tri-p-tolylphosphine in chloroform as solvent. The complexes of the type [HgX2(p-tolyl)3PCHCOC6H4CH3)] (X = Cl, Br and I) are prepared by the reaction of title ylide with mercury(II) halides in good yields, using methanol as solvent. The final products were characterized by IR, 1H, 13C, 31P NMR spectroscopic methods and microanalysis.