Methyl isocyanide complexes of a trinuclear platinum cluster: a model for chemisorption of isocyanides on platinum surfaces. Crystal structure of [Pt3(CNMe)2-(µ-Ph2PCH2PPh2)3][PF6]2·3Me2CO
The complex cation [Pt3(µ3-CO)(µ-dppm)3]2+1, dppm = Ph2PCH2PPh2, reacts with 1 equivalent of MeNC to give an intermediate [Pt3(CNMe)(µ-CO)(µ-dppm)3]2+2, which then rearranges to [Pt3(CNMe)(η3-CO)(η-dppm)3]2+3. Reaction with a second equivalent of MeNC leads to displacement of CO and formation of [Pt3(CNMe)2(µ-dppm)3]2+4. Excess of MeNC reacts with 1 or 4 to displace a platinum(0) fragment and form [Pt2(CNMe)2(µ-dppm)2]2+7, [Pt2(CNMe)2(µ-CNMe)(µ-dppm)2]2+8, and [Pt2(CNMe)3(µ-dppm)2]2+9. Complexes 8 and 9 easily lose MeNC to give 7. The complexes have been characterized by IR and by 1H, 13C, 31P and 195Pt 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.