Ligand substitution behavior of Ru₆(μ₆-C)(CO) ₁₇ with unsaturated diphosphines: Facile capping of a polyhedral face and photochemically promoted P-C bond cleavage in the cluster Ru ₆(μ₆-C)(CO)₁₄(μ₃-bpcd)

The ligand substitution chemistry of the hexaruthenium cluster Ru ₆(μ₆-C)(CO)₁₇ (1) with several unsaturated diphosphine ligands has been investigated. Thermolysis of 1 with (Z)-Ph ₂PCHCHPPh₂ (dppen) furnishes the new cluster compounds Ru₅(μ₅-C)(CO)₁₂(μ₃-dppen) (2), Ru₆(μ₆-C)(CO)₁₄(μ₃-dppen) (3), and Ru₆(μ₆-C)(CO)₁₂(μ₃- dppen)(μ-dppen) (4). Clusters 2 and 3 are also obtained when a mixture of 1 and dppen is treated with the oxidative-decarbonylation reagent Me ₃NO. Thermolysis or Me₃NO activation of 1 in the presence of 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) yields Ru ₆(μ₆-C)(CO)₁₄(μ₃-bpcd) (4) as the sole observable product. Near-UV irradiation of 4 leads to P-C bond cleavage and the formation of phosphido-bridged cluster Ru₆(μ₆- C)(CO)₁₃[μ₃-CC(PPh₂)C(O)CH ₂C(O)](μ-PPh₂) (6) in essentially quantitative yield. The reaction between 1 and the ligand 3,4-bis(diphenylphosphino)-5-methoxy-2(5H) -furanone (bmf) leads to the formation of Ru₆(μ₆-C)(CO) ₁₄(μ₃-bmf) (7), which exists as a single diastereomer in solution as shown by ¹H and ³¹P NMR spectroscopy. The molecular structures and the binding mode of the ancillary diphosphine ligand(s) in 2-7 have all been established by X-ray diffraction analyses. The solid-state structure of 7 reveals that the chiral bmf ligand caps one of the metallic faces stereospecifically with the 5-methoxy moiety oriented distal or trans relative to the Ru₆ polyhedral core. The new substitution products are discussed relative to the products obtained from 1 and the related diphosphine ligands dppm, dppe, dppf, and dppbz.