TRINUCLEAR AND TETRANUCLEAR PLATINUM-IRIDIUM CLUSTER COMPLEXES - A REMARKABLE METAL FOR METAL SUBSTITUTION-REACTION

The reaction of [Pt-3(mu 3-CO)(mu-dPPm)(3)](2+), 1, dppm = Ph2PCH2PPh2 , with [Ir(CO)(4)](-) at low temperature gives [Pt-3(mu(3)-CO)(mu-dppm )(3){Ir(CO)(4)}](+), 2, and subsequent loss of CO leads to the butterf ly complex [Pt-3{Ir(CO)(mu-CO)(2)}(mu-CO)(mu-dppm)(3)](+), 3. Complex 3 reacts with L = P(OPh)(3) to give [Pt-3{IrL(mu-CO)(2)}(mu-CO)(mu-dpp m)(3)](+), 4, which has been characterized by X-ray structure determin ation and has a butterfly structure with iridium at a wingtip position . Cluster 3 is thermally unstable and rearranges in solution to form t he isomeric butterfly cluster cation [Pt2Ir{Pt(CO)(mu-CO)(2)}(CO)(mu-d ppm)(3)](+), 5, in which the iridium atom now occupies a hinge positio n and whose formation involves phosphorus migration from platinum to i ridium. Under CO, 5 eliminates one platinum atom to form the trimetall ic complex [Pt2Ir(mu(3)-CO)(CO)(mu-dppm)(3)](+), 6. The overall reacti on then involves displacement of a platinum atom from the 42-electron cluster cation 1 by {IrCO}(-) to give the 44-electron cation 6.