Clusters Containing a Quadruply Bridging CO Ligand. Syntheses, Crystal Structures, and Solution Dynamics of CpWRu₄(CO)₁₄H and Cp*MRu₄(CO)₁₄H (M = Mo, W)

The pentametal carbonyl cluster compounds CpWRu₄(CO)₁₄(μ₃-H) (4), Cp*MoRu₄(CO)₁₄-(μ₃-H) (5), and Cp*WRu₄(CO)₁₄(μ₃-H) (6) were obtained by condensation of Ru₃(CO)₁₂ with the corresponding anionic reagents [CpW(CO)₃][PPN] and [Cp*M(CO)₃][PPN] (M = Mo,' W) in the ratio 3:2 in refluxing THF solution, followed by treatment with excess CF₃CO₂H in CH₂Cl₂ at room temperature. The Cp derivative 4 possesses a trigonal-bipyramidal Ru₄W core in which the W atom is located at an equatorial position and the hydride lies on a Wru ₂triangular face. In contrast, the Cp* derivatives 5 and 6 adopt an edge-bridged tetrahedral geometry with a tentacle Cp*M fragment bridging a Ru-Ru edge, on which the novel μ₄-η²-CO ligand is associated with the local butterfly Ru₃M array (M = Mo, W). The solution dynamics of these three cluster compounds are discussed.