Synthesis, reactivity, and spectroscopic studies of some tetranuclear osmium clusters. Structural characterization of [Os4H(CO)12{µ3-NC(O)Me}{M(PPh3)}](M = Au or Cu) and [N(PPh3)2][Os4H2(CO)12I]

The interaction of [Os4H3(CO)12(NCMe)2][BF4](1) with [N(PPh3)2][X](X = NO2, Cl, Br, or l) affords the species [N(PPh3)2][Os4H(CO)12{µ3-NC(O)Me}](2)(X = NO2), [Os4H3(CO)12(µ-X)][X = Cl (6), Br (7), or l (8)], and [N(PPh3)2][Os4H2(CO)12X][X = Cl (9), Br (10), or l (11)] which were characterized by i.r. and 1H n.m.r. spectroscopy. The reaction of complex (1) with nitrite ion results in a novel interaction which involves oxygen transfer from the nitrite ion and conversion of a co-ordinated NCMe ligand into an amido group on the cluster surface. The anionic species (2) reacts with [M(PPh3)]+ to yield the neutral mixed-metal clusters [Os4H(CO)12{µ3NC(O)Me}{M(PPh3)}][M = Au (3) or Cu (4)] which have been structurally characterized by single-crystal X-ray diffractometry. This shows that they possess a butterfly metal framework capped by the heterometallic fragment and µ3-bridged by the four-electron-donor amido group. Complexes (3) and (4) are isomorphous, monoclinic, with space group C2/c and Z= 8: (3), a= 25.681(7), b= 16.069(1), c= 18.265(2)A, and β= 90.90(1)°(4)a= 25.318(6), b= 15.964(5), c= 18.347(7)A, and β= 91.80(2)°. Spectroscopic data suggest that compounds (6) and (7) also possess a butterfly metal framework with a bridging, three-electron-donor, halide ligand, while the anionic species (11) possesses a tetrahedral arrangement of metal atoms with a terminally co-ordinated iodide ligand, as shown by X-ray diffractometry: monoclinic, space group P21/a, Z= 8, a= 16.841(2), b= 20.699(1), c= 29.249(3), and β= 90.91(2)°. Protonation of (11) yields the neutral species [Os4H3(CO)12(µ-l)], showing that facile reversible tetrahedral–butterfly interconversion is assisted by a change in co-ordination mode and electron donation of the l atom. The reaction of compound (11) with CF3SO3R (R = Me or Et) was monitored by 1H n.m.r. spectroscopy and the results explained in terms of the formation of alkyl iodide derivatives.