Hexafluoroacetone reacts with the zero-valent compounds [Ph3P]4M (M = Pt or Pd) to afford the complexes [Ph3P]2M[(CF3)2CO]. The compounds [Ph3P]2Pt[(CF2Cl)2CO] and [Ph2PMe]2Pt[(CF3)2CO] have been similarly prepared. Related iridium(III) complexes are also described, as are stable iridium(III) derivatives with 1,1-dicyano-2,2-bis(trifluoromethyl)ethylene, hexafluoropropene, and bromotrifluoroethylene as ligands. The infrared and 19F n.m.r. spectra of these complexes suggest the presence of three-membered ring systems involving the metal atom.