Addition of Pt(PBu^t₃) groups to Ru ₅(CO)₁₂(η⁶-C₆H ₆)(μ₅-C). Synthesis, structures, and dynamical activity

The reaction of Ru₅(CO)₁₂(η⁶-C ₆H₆)(μ₅-C), 7, with Pt(PBu^t ₃)₂ yielded two products Ru₅(CO) ₁₂(η⁶-C₆H₆)(μ₆-C) [Pt(PBu^t₃)], 8, and Ru₅(CO)₁₂(η ⁶-C₆H₆)(μ₆-C)[Pt(PBu ^t₃)]₂, 9. Compound 8 contains a Ru ₅Pt metal core in an open octahedral structure. In solution, 8 exists as a mixture of two isomers that interconvert rapidly on the NMR time scale at 20 °C, ΔH‡ = 7.1(1) kcal mol^-1, ΔS‡ = -5.1(6) cal mol^-1 K^-1, and ΔG₂₉₈‡ = 8.6(3) kcal mol^-1. Compound 9 is structurally similar to 8, but has an additional Pt(PBu^t₃) group bridging an Ru-Ru edge of the cluster. The two Pt(PBu^t₃) groups in 9 rapidly exchange on the NMR time scale at 70 °C, ΔH‡ = 9.2(3) kcal mol^-1, ΔS‡ = -5(1) cal mol^-1 K^-1, and ΔG₂₉₈‡ = 10.7(7) kcal mol^-1. Compound 8 reacts with hydrogen to give the dihydrido complex Ru₅(CO) ₁₁(η⁶-C₆H₆)(μ₆-C) [Pt(PBu^t₃)](μ-H)₂, 10, in 59% yield. This compound consists of a closed Ru₅Pt octahedron with two hydride ligands bridging two of the four Pt-Ru bonds.