A reversible metal framework rearrangement in high-nuclearity osmium–platinum cluster compounds. X-Ray crystal structures of [Os6Pt(CO)17(µ3-NCMe)(C8H12)], [Os6Pt(CO)17(µ4-NCMe)(C8H12)](C8H12= cyclo-octa-1,5-diene), and [Os6(CO)19(µ3-NCMe)]: compounds with novel metal–acetonitrile bonding modes

Abstract

The reaction of [Os₆(CO)₁₇(NCMe)] with [Pt(C₈H₁₂)₂](C₈H₁₂= cyclo-octa-1,5-diene) results in the formation of [Os₆Pt(CO)₁₇(µ₃-NCMe)(C₈H₁₂)](1). The geometry of (1) may be derived from that of [Os₆(CO)₁₈] by breaking one Os–Os edge and adding a terminal Pt(C₈H₁₂) fragment to one of the Os atoms constituting the central tetrahedron. Upon standing in CH₂Cl₂, cluster (1) isomerizes to a different geometry, [Os₆Pt(CO)₁₇(µ₄-NCMe)(C₈H₁₂)](2). The isomerization process is first order with ΔH^‡= 28.7 kcal mol^–1 and ΔS^‡= 13 cal K^–1 mol^–1. The structure of isomer (2) may be derived from its precursor (1) by breaking one more Os–Os edge and by moving the Pt(C₈H₁₂) unit into a bridging position. Substitution of the C₈H₁₂ ligand in (1) or (2) by 1,2-bis(diphenylphosphino)ethane or P(OMe)₃ results in clusters having a metallic framework analogous to (1). The extrusion of the Pt moiety results from reaction of CO with either isomer giving a product characterized as [Os₆(CO)₁₉(µ₃-NCMe)](3).