METHYL ISOCYANIDE COMPLEXES OF A TRINUCLEAR PLATINUM CLUSTER - A MODEL FOR CHEMISORPTION OF ISOCYANIDES ON PLATINUM SURFACES - CRYSTAL-STRUCTURE OF [PT3(CNME)2-(MU-PH2PCH2PPH2)3][PF6]2.3ME2CO

The complex cation [Pt3(mu-3-CO)(mu-dppm)3]2+ 1, dppm = Ph2PCH2PPh2, reacts with 1 equivalent of MeNC to give an intermediate [Pt3(CNMe)(mu-CO)(mu-dppm)3]2+ 2, which then rearranges to [Pt3-(CNMe) (eta-3-CO)(eta-dppm)3]2+ 3. Reaction with a second equivalent of MeNC leads to displacement of CO and formation of [Pt3(CNMe)2(mu-dppm)3]2+ 4. Excess of MeNC reacts with 1 or 4 to displace a platinum(0) fragment and form [Pt2(CNMe)2(mu-dppm)2]2+ 7, [Pt2(CNMe)2(mu-CNMe)(mu-dppm)2]2+ 8, and [Pt2(CNMe)3(mu-dppm)2]2+ 9. Complexes 8 and 9 easily lose MeNC to give 7. The complexes have been characterized by IR and by H-1, C-13, P-31 and Pt-195 NMR spectroscopies and 4 has also been characterized crystallographically. Complex 4 is an unusual 44-electron cluster which contains two approximately square-planar fragments and one octahedral platinum fragment forming the Pt3 triangle, and with no single-atom bridging group. Complexes 3 and 4 are fluxional such that they appear to attain three-fold symmetry by a process in which the isocyanide ligands migrate easily around the Pt3 triangle. It is suggested that the binding of isocyanides in the Pt3 clusters resembles the binding to a Pt(111) surface, and that the fluxionality models the mobility of isocyanide ligands on a platinum surface.