Metals in organic syntheses XI. 31P NMR and reactivity studies on the system trans-[PtCl(CO-n-hexyl)(PPh3)2]-SnCl2, an active intermediate in the catalytic hydroformylation of 1-hexene

The system trans-[PtCl(CO-n-hexyl)(PPh3)2]/SnCl2 has been investigated by 31P NMR spectroscopy. In CD2Cl2 or acetone-d6 solutions two species (in equilibrium with the starting Pt complex) are observed at low temperature: one set of signals is attributed to the complex trans-[Pt(SnCl3)(CO-n-hexyl)(PPh3)2]; the other set does not show SnP coupling and it is tentatively attributed to a complex having chloride bridging the Pt and Sn metal centers. Formation of the complex trans-[Pt(SnCl3)(CO-n-hexyl)(PPh3)2] is prevented when ethanol is added to the CD3Cl2 are acetone-d6 solutions. Treatment of the CD2Cl2 or acetone-d6 solution with molecular hydrogen give n-heptanal and hydroplatinum species; this reaction does not occur in the presence of ethanol, where only a complex having chloride bridging the Pt and Sn metal centers seems to be present. The result are discussed in connection with the catalytic cycle of olefin hydroformylation promoted by the [PtCl2(PPh3)2]/SnCl2 system.