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(PBut3)2 at room temperature yielded the mixed-metal cluster complex
PtRu5(CO)15(PBut3)(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(PBut3)2 with compound 1 yielded two new cluster complexes:  PdRu5(CO)15(PBut3)(μ6-C), 3, in 50% yield and
Pd2Ru5(CO)15(PBut3)2(μ6-C), 4, in 6% yield. The yield of 4 was increased to 47% when an excess of Pd(PBut3)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(PBut3) grouping
that is capping a triangular face of the ruthenium cluster. The Pd(PBut3) 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.