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

Abstract

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.