Remarkable dynamical opening and closing of platinum and palladium pentaruthenium carbido carbonyl cluster complexes

The reaction of Ru₅(CO)₁₅(μ₅-C), 1, with Pt(PBu^t₃)₂ at room temperature yielded the mixed-metal cluster complex PtRu₅(CO)₁₅(PBu^t₃)(C), 2, in 52% yield. Compound 2 consists of a mixture of two interconverting isomers in solution. One isomer, 2A, can be isolated by crystallization from benzene/octane solvent. The second isomer, 2B, can be isolated by crystallization from diethyl ether. Both were characterized crystallographically. Isomer 2A consists of a square pyramidal cluster of five ruthenium atoms with a phosphine-substituted platinum atom spanning the square base. Isomer 2B consists of a square pyramidal cluster of five ruthenium atoms with a phosphine-substituted platinum atom on an edge on the square base. The two isomers interconvert rapidly on the NMR time scale at 40 °C, ΔG₃₁₃‡ = 11.4(8) kcal mol^-1, ΔH‡ = 8.8(5) kcal mol^-1, ΔS‡ = -8.4(9) cal mol^-1 K^-1. The reaction of Pd(PBu^t₃)₂ with compound 1 yielded two new cluster complexes: PdRu₅(CO)₁₅(PBu^t₃)(μ6-C), 3, in 50% yield and Pd₂Ru₅(CO)₁₅(PBu^t ₃)₂(μ6-C), 4, in 6% yield. The yield of 4 was increased to 47% when an excess of Pd(PBu^t₃)₂ was used. In the solid state compound 3 is structurally analogous to 2A, but in solution it also exists as a mixture of interconverting isomers; ΔG₂₉₈‡ = 10.6(6) kcal mol^-1, ΔH‡ = 9.7(3) kcal mol^-1, and ΔS‡ = -3(1) cal mol^-1 K^-1 for 3. Compound 4 contains an octahedral cluster consisting of one palladium atom and five ruthenium atoms with an interstitial carbido ligand in the center of the octahedron, but it also has one additional Pd(PBu^t₃) grouping that is capping a triangular face of the ruthenium cluster. The Pd(PBu^t₃) groups in 4 also undergo dynamical interchange that is rapid on the NMR time scale at 25°C; ΔG₂₉₈‡ = 11(1) kcal mol-1, ΔH‡ = 10.2(4) kcal mol^-1, and ΔS‡ = -3(2) cal mol^-1 K^-1 for 4.