High-Nuclearity Phosphinidene Clusters. Synthesis, Characterization, and Reactivity of Two W₂Ru₄ Clusters with a μ₄-η²-CO Ligand

Thermolysis of the heterometallic phosphinidene cluster Cp*WRu₂(CO)₈(μ.-H)(μ₃-PPh) (2) in refluxing toluene solution gave two W₂Ru₄ clusters (4 and 5) via elimination of one H₂ and four CO molecules. Complexes 4 and 5 are isomers, which adopt a square-pyramidal WRu₄ core skeleton with a pendant W atom bridging a Ru-Ru edge, on which the unusual μ₄-η²-CO ligand is associated with the butterfly W₂Ru₂ array; one μ₄-PPh ligand occupies a WRu₃ square face in both isomers, while a second μ3-PPh ligand caps a Ru₃ face in 4 and a WRu₂ face in 5. In refluxing toluene solution 4 and 5 began to equilibrate via a process involving μ₃-PPh migration. When a solution of 4 was treated with dihydrogen, cluster degradation occurred to regenerate a small amount of 2 and tetranuclear Cp*WRu₃(CO)₁₀(μ₃-PPh)(μ₃-H) (3). Similarly, compound 4 reacts with carbon monoxide at 4 atm to produce the homometallic phosphinidene compounds Ru₃(CO)₉(μ₃-PPh)₂ (6) and Ru₄(CO)₁₁(μ₄-PPh)₂ (7) in moderate yield. Crystal data for 4: space group P2₁/n; a = 12.174(4), b = 17.427(5), c = 22.773(6) Å; β = 100.21(2)°; Z = 4; 5016 observed reflections; R = 0.034. Crystal data for 5: space group C2/c; a = 45.527(5), b = 10.201(1), c = 21.906(9) Å, β = 93.90(3)°; Z = 8; 5448 observed reflections; R = 0.033.