A reversible metal framework rearrangement in high-nuclearity osmium–platinum cluster compounds. X -Ray crystal structures of [Os 6 Pt(CO) 17 (µ 3 -NCMe)(C 8 H 12 )], [Os 6 Pt(CO) 17 (µ 4 -NCMe)(C 8 H 12 )](C 8 H 12 = cyclo-octa-1,5-diene), and [Os 6 (CO) 19 (µ 3 -NCMe)]: compounds with novel metal–acetonitrile bonding modes

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).