Reactions of alkynes with [Os₃(CO)₁₁(NCCH₃)]: The crystal structures of [Os₃(CO)₉(C₃H₂OH)H] and [Os₃(CO)₉(C₃H₂OCH₃)H]

The reaction of [Os₃(CO)₁₁(NCCH₃)] with hydrous C₂H₂, CH₃C≡CH, or PhC≡CH yields, as the major product, [Os₃(CO)₉(RC₃H₂O)H] (R = H, CH₃, or C₆H₅). The backbone of the organic ligand, an allyl alcohol, is formed from an alkyne molecule and a CO ligand from the cluster. It bonds to a face of the triangular cluster through two σ bonds and one π-allyl bond. The complexes exist in two isomeric forms which have not been separated. The complex [Os₃(CO)₉(C₃H₂OH)H] crystallizes in space group Pbca with a = 16.291(5), b = 16.861(5), c = 12.234(3) Å, and Z = 8. Its structure has been solved by a combination of direct methods and Fourier-difference techniques, and refined by full-matrix least squares to an R of 0.060 for 1 327 diffractometer data. Both isomers co-crystallize in this complex, and the structure shows that the organic ligand is disordered, preventing an assessment of the nature of the isomers. Conversion of the allyl alcohol ligand into an allyl methyl ether has allowed the determination of one of the isomers. Thus [Os₃(CO)₉(C₃H₂OCH₃)H] crystallizes in space group P2₁/n with a = 6.975(3), b = 30.960(6), c = 8.695(4) Å, β = 107.62(2)°, and Z = 4. Its structure has been solved by a combination of direct methods and Fourier-difference techniques, and refined by full-matrix least squares to an R of 0.053 for 1 671 diffractometer data. The two isomers in the [Os₃(CO)₉(RC₃H₂O)H] molecules are thought to be due to restricted rotation about the C-O bond of the alcohol, giving rise to two possible orientations for the O-H proton. Only one of these orientations is accessible to the allyl methyl ether derivative.