New High Nuclearity Platinum−Ruthenium Carbonyl Cluster Complexes Containing a Phenylacetylene Ligand:  Structures and Properties

Reaction of the mixed-metal carbonyl cluster complex Ru₅(CO)₁₅(C)[Pt(PBu^t₃)], 3, with PhC₂H yielded the new compound PtRu₅(CO)₁₃(PBu^t₃)(μ₅-C)(μ₃-PhC₂H), 4, in 41% yield. Two new bimetallic cluster complexes, Pt₂Ru₅(CO)₁₃(PBu^t₃)₂(μ₅-C)(μ₃-PhC₂H), 5, and Pt₃Ru₅(CO)₁₃(PBu^t₃)₃(μ₅-C)(μ₃-PhC₂H), 6, were subsequently obtained in 44% and 40% yield, respectively, from the reaction of 4 with an excess of Pt(PBu^t₃)₂. All products were characterized crystallographically by single-crystal X-ray diffraction techniques. The structure of 4 consists of a square-pyramidal cluster of five ruthenium atoms with a Pt(PBu^t₃) group capping one of the Ru₃ triangles. A PhC₂H ligand bridges one of the PtRu₂ triangles. Compounds 5 and 6 are similar to 4 but have in addition one and two Pt(PBu^t₃) groups bridging one and two edges of the Ru₅ square-pyramidal portion of the cluster. Compound 6 was shown to be dynamically active on the ³¹P NMR time scale by a process that involves an interchange of two of its inequivalent Pt(PBu^t₃) groups.