Synthesis and Spectroscopic Characterization of H₃CoRu₃(CO)₁₂. Crystal and Molecular Structure of the C_3v Isomer

The reaction of HCoRu₃(CO)₁₃ with H₂ in refluxing hexane gives the new cluster H₃CoRu₃(CO)₁₂ in 75% yield. Infrared and NMR spectra indicate that the cluster exists in two isomeric forms. The structure of one isomer has been determined by single-crystal X-ray diffraction. It crystallizes in the triclinic space group P1 with a = 9.204 (2) Å, b = 13.615 (4) Å, c = 8.318 (2) Å, a = 100.49 (2)°, β = 111.51 (2)°, γ = 81.78 (2)°, V = 950.1 ų and Z = 2. The structure was determined by the heavy-atom method and refined to R₁ = 2.3% and R₂ = 3.6%. The CoRu₃ core of the molecule defines a distorted tetrahedron with three carbonyls terminally bound to each metal atom. The hydride ligands were located by difference Fourier techniques and bridge the three Ru-Ru bonds. The overall symmetry of the cluster is approximately C_3v. Spectral evidence indicates that the second isomer contains a bridging CO ligand and three nonequivalent hydrogens. The interconversion of the two isomers and the various hydrogen-exchange processes have been monitored by ¹H NMR spectroscopy, and the exchange mechanisms are discussed.