Ligand substitution reactons in electron-rich clusters. the synthesis, structures, and bonding of Os₄(CO)₁₂L(μ₃-S)₂ and Os₄(CO)₁₁L(μ₃-S)₂ (L = PMe₂Ph and CN-t-Bu)

The compounds Os₄(CO)₁₂L(μ3-S)₂ (2a, L = PMe₂Ph; 2b, L = CN-t-Bu) have been synthesized by ligand addition to Os₄(CO)₁₂(μ₃-S)₂ (1). Both compounds have been characterized by single-crystal X-ray diffraction analyses. For 2a: space group P2₁/a, a = 17.941 (8) Å, b = 8.957 (3) Å, c = 17.949 (7) Å, β= 99.75 (4)°, Z = 4, ρ_calcd = 3.04 g/cm³. The structure was solved by direct methods and refined (3542 reflections) to the final values for the residuals R_F = 0.041 and R_wF = 0.046. For 2b: space group P2₁/n, a = 15.113 (6) Å, b = 10.798 (9) Å, c = 18.659 (6) Å, β= 102.33 (3)°, Z = 4, ρ_calcd = 2.87 g/cm³. The structure was solved by direct methods and refined (1939 reflections) to the final values of the residuals R_F = 0.047 and R_wF = 0.050. Both 2a and 2b contain open-planar clusters of four osmium atoms with three metal-metal bonds. Triply bridging sulfido ligands are symmetrically disposed on each side of the Os₄ plane. When heated to 125°C, 2a and 2b lose CO and are converted in high yield to Os₄(CO)₁₁L(μ₃-S)₂ (3a, L = PMe₂Ph; 3b, L = CN-t-Bu). 3a and 3b were both characterized by single-crystal X-ray diffraction analyses. For 3a: space group P1, a = 8.994 (5) Å, b = 10.057 (3) Å, c = 15.048 (7) Å, α = 99.62 (4)°, β = 92.22 (4)°, γ = 92.55 (5)°, Z = 2, ρ_calcd = 3.15 g/cm³. The structure was solved by the heavy-atom method and refined (3110 reflections) to the final values of the residuals R_F = 0.040 and R_wF = 0.046. For 3b: space group Pbca, a = 23.819 (15) Å, b = 11.524 (10) Å, c = 18.497 (9) Å, Z = 8, ρ_calcd = 3.18 g/cm³. The structure was solved by direct methods and refined (1815 reflections) to the final values of the residuals R_F = 0.042 and R_wF = 0.039. 3a and 3b both contain butterfly tetrahedral clusters of four metal atoms with triply bridging sulfido ligands on the two open-triangular faces. In both compounds two of the five metal-metal bonds are elongated, but in 3a they are nearly equal in length, 2.987 (1) and 3.013 (1) Å, while in 3b they are significantly different length, 2.965 (1) and 3.115 (1) Å. © 1984 American Chemical Society.