Reaction of ketenylidenetriphenylphosphorane (Ph(3)P=C=C=O) with platinum(II) and palladium(II) complexes. Synthesis, characterization, and molecular structure of [Pt(eta(3)-C3H5){eta(1)-C(PPh(3))(CO)}(PPh(3))]BF4

Ketenylidenetriphenylphosphorane, Ph(3)P=C=C=O, reacts with Pt(II) and Pd(II) eta(3)-allyl complexes (allyl = C3H5, 2-MeC(3)H(4)) to give neutral or cationic mononuclear eta(1)-ketenyl derivatives [M(eta(3)-allyl){(eta(1)-C(PPH3)(CO)}](m+) (L = Cl, m = 0; L = PPh(3), m = 1) that have been characterized by elemental analysis, IR, and multinuclear NMR. The X-ray molecular structure determination performed on a single crystal of the air-stable derivative [Pt(eta(3)-C3H5){eta(1)-C(PPh(3))(CO)}(PPh(3))]-BF4 furnishes the first crystallographic evidence of an eta(1)-ketenyl derivative in which the ketene moiety is also involved in an ylide grouping.