Synthesis and characterization of tetranuclear mixed-metal hydride complexes, LWM₃(CO)₁₁(μ-H)₃, L = C₅H₅, C₅Me₅ and M = Ru, OS

Hydrogenation of the tetranuclear mixed-metal clusters LWM₃(CO)₁₂(μ-H) (L = C₅H₅, M = Os, (1); L = C₅Me₅, M = Os, (2); L = C₅H₅, M = Ru, (3); L = C₅Me₅, M = Ru, (4)) in toluene solution has yielded the tetrahedral cluster complexes LWM₃(CO)₁₁(μ-H)₃ (L = C₅H₅, M = Os, (5); L = C₅Me₅, M = Os, (6); L = C₅H₅, M = Ru, (7); L = C₅Me₅, M = Ru, (8)). Complex 8 was characterized by single crystal X-ray diffraction. Crystal data for 8: space group P21n ; a = 10.731(4), b = 16.275(4), c = 15.606(4) Å, β = 99.76(2)°, Z = 4; R_F = 0.0255, R_w = 0.0245 and GOF = 1.19. Complexes 6 and 8, which possess a Cp*W(CO)₂ fragment, are present solely as one isomer in solution. The structure of this isomer (denoted a) is consistent with the solid state structure of 8 in which the hydride ligands are located on the edges of a WM₂ triangular face. For complexes 5 and 7, each containing a CpW(CO)₂ fragment, variable temperature ¹H NMR studies suggest the presence of two rapidly interconverting isomers (a and b) in solution. Isomer b contains a tetrahedral core similar to isomer a, but in b, the hydride ligands occupy two MHM sites and one WHM site, in a zigzag arrangement.