Subtlety in the reactivity of a diketo phosphorus ylide towards mercuric halides: the unprecedented O-coordination of alpha-acetyl-alpha-benzoylmethylenetriphenylphosphorane to Hg(II)

The reactions of the title ylide with HgX2 (X = Cl, Br or I) lead to the re giospecific binding of the acetyl oxygen to soft Hg(ii), producing a chloro complex with (2 + 2) coordination and isostructural dimeric bromo and iodo complexes containing halogen bridges with tetrahedral configurations aroun d the metal centres.