Cleavage of Metal-Metal Bonds in Heteronuclear Clusters. Reactions of Os₃(μ₃-S)(μ₃-η²-SCH₂)(CO)₈(PMe₂Ph) with HCl and P(OMe)₃

The reactions of the cluster Os₃(μ₃-S)(μ₃-η²-SCH₂)(CO)₈(PMe₂Ph) (I), which contains a thioformaldehyde ligand, with HCl and P(OMe)₃ have been investigated. The reaction of I with HCl yields an addition product HOs₃(μ₃-S)(μ₃-η²-SCH₂)(CO)₈(PMe₂Ph)Cl (II), which has been characterized by X-ray crystallographic methods: space group P2₁/c, at 23 °C; a = 10.423 (2) Å, b = 11.014 (5) Å, c = 22.743 (9) Å, β = 101.98 (3); V = 2554 (3) ų; Z = 4; ρ_calcd = 2.72 g/cm³. For 2689 reflections (F_o ≥ 3.0 σ(F_o²)) R₁ = 0.044 and R₂ = 0.048. The molecule contains a group of three osmium atoms but only one osmium-osmium bond. The third osmium is linked to the others by a triply bridging sulfide and triply bridging thioformaldehyde ligand. The addition of HCl to I results in cleavage of one of its osmium-osmium bonds. The reaction of I with P(OMe)₃ yields the new molecule Os₃(μ₃-S)(μ₃-η²-SCH₂)(CO)₇(PMe₂Ph)[P(OMe)₃] (III). III was also analyzed by an X-ray crystallographic analysis: space group P1, at 23 °C; a = 10.694 (2) Å, b = 11.630 (3) Å, c = 12.675 (2) Å, α = 111.16 (2)°, β = 99.63 (2)°, γ = 92.36 (2)°; V = 1441 (1) ų; Z = 2; ͡_calcd = 2.55 g/cm³. For 4083 reflections (F_o ≥ 3.0σ(F_o²)) R₁ = 0.035 and R₂ = 0.038. III is formed from I by the substitution of one of the carbonyl ligands on the phosphine-substituted osmium atom with the P(OMe)₃ ligand. Thus, as in I, III contains a cluster with two osmium-osmium bonds a triply bridging sulfide ligand and a triply bridging thioformaldehyde ligand. The nature of the formations of II and III is compared in terms of probable mechanisms.