The reaction of Ru-5(CO)(12)(eta(6)-C6H6)(mu(5)-C), 7, with Pt(PBu3t)(2) yielded two products Ru-5(CO)(12)(eta(6)-C6H6)(mu(6)-C)[Pt-(PBu3t)], 8, and Ru-5(CO)(12) (eta(6)-C6H6)(mu(6)-C)[Pt(PBu3t)](2), 9. Compound 8 contains a Ru5Pt 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 degreesC, DeltaH(double dagger) = 7.1 (1) kcal mol(-1), DeltaS(double dagger) = -5.1(6) cal mol(-1) K-1, and DeltaG(298)(double dagger) = 8.6(3) kcal mol(-1). Compound 9 is structurally similar to 8, but has an additional Pt(PBu3t) group bridging an Ru-Ru edge of the cluster. the two Pt(PBu3t) groups in 9 rapidly exchange on the NMR time scale at 70 degreesC, DeltaH(double dagger) = 9.2(3) kcal mol(-1), DeltaS(double dagger) = -5(1) cal mol(-1) K-1, and DeltaG(298)(double dagger) = 10.7(7) kcal mol(-1). Compound 8 reacts with hydrogen to give the dihydrido complex Ru-5(CO)(11)(eta(6)-C6H6)(mu(6)-C)[Pt(PBu3t)](mu-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.