Synthesis and properties of mixed-metal phosphido and phosphinidene clusters derived from reaction between Ru₃(CO)₁₀(μ-H)(μ-PPh₂) and Cp* Mo(CO)₃H

The tetranuclear phosphido cluster Cp* MoRu₃(CO)₁₀(μ-H)₂(μ-PPh₂) (5) and the phosphinidene cluster Cp* MoRu₃(CO)₁₀(μ₃-H) (μ₃-PPh) (6) have been synthesized by reaction of Ru₃(CO)₁₀(μ-H)(μ-PPh₂) with excess molybdenum hydride Cp* Mo(CO)₃H in refluxing toluene solution. Crystals of 5 are monoclinic, space group P 2₁ with a = 10.708(2), b = 10.848(4), c = 14.885(2) Å, β = 97.63(2)°, Z = 2, R = 0.021, R_w = 0.019 for 3025 observed reflections. The cluster has a tetrahedral array of metal atoms with one edge-bridging and one face-bridging hydride, and a phosphido ligand bridged across a basal Ru-Ru edge. Thermolysis of 5 under similar conditions produced the phosphinidene cluster 6 in high yield via elimination of a benzene molecule, indicating that 5 is an intermediate in the formation of 6. Subsequent treatment of 6 with CO caused fragmentation of the cluster affording a trinuclear phosphinidene cluster Cp* MoRu₂(CO)₈(μ-H)(μ₃-PPh) (7). Dimerization of 7 occurred upon thermolysis to afford hexanuclear Cp₂* Mo₂Ru₄(CO)₁₂(μ-PPh)₂ (8), which has also been characterized by X-ray diffraction. Crystal data of 8: space group C 2/c; a = 45.333(7), b = 10.185(2), c = 21.915(8) Å, β = 93.82(3)°, Z = 8. The structure was solved by direct method and refined to R and R_w of 0.035 and 0.030 for 6135 observed reflections with I > 2σ-(I). The molecule adopts a square pyramidal MoRu₄ skeleton with a tentacle Mo atom bridging a Ru-Ru edge, on which the novel μ₄-η²-CO ligand is associated with the butterfly Mo₂Ru₂ array; one μ₄-PPh ligand occupies a MoRu₃ square face and a second μ₃-PPh ligand caps a MoRu₂ face.