New alkyne bridged mixed-metal clusters and studies of their activity for catalytic hydrosilylation of alkynes

The homologous series of compounds MPt2(CO)(5)(PPh3)(2)(PhC2Ph), M = Fe (1), M = Ru (3) and M = Os (4) were obtained in the yields 55%, 24% and 30% from the reactions of Pt(PPh3)(2)(PhC2Ph) with Fe(CO)(5), Ru-3(CO)(10), and Os(CO)(5), respectively. Each of the products was characterized by IR, elemental analysis and a single crystal X-ray diffraction analysis. A second mixed-metal cluster product, Ru2Pt(CO)(7)(PPh3)(2)(PhC2Ph) (2) (45% yield) was also obtained from the reaction that yielded 3. In fact, it is obtained in a higher yield than that of 3. Compounds 1, 3, and 4 are isostructural and are comprised of a MPt2 (M = Fe, Ru or Os) triangular metal cluster containing a triply bridging diphenylacetylene ligand. The structure of compound 2 is similar to that of 1, 3, and 4, but contains two ruthenium and one platinum atom in the triangular cluster. One coproduct Os(CO)(2)(PPh3)(2)(PhC2Ph) (5) (25% yield) was obtained from the reaction of Os(CO)(5) with Pt(PPh3)(2)(PhC2Ph). Compound 5 contains only one metal atom with an approximately trigonal bipyramidal coordination having the two phosphine ligands in the axial positions and the alkyne in an equatorial site. The reaction of 2 with H-2 in refluxing hexane afforded the tetranuclear complex H2Ru2Pt2(CO)(8)(PPh3)(2) (6) (11% yield) that contains an Ru2Pt2 tetrahedral shaped cluster with two bridging hydride ligands. The ability of the solutions of compounds 1-6 and Pt(PPh3)(2)(PhC2Ph) to produce catalytic hydrosilylation of diphenylacetylene by triethylsilane to yield (E)-[(1,2-diphenyl)ethenyl]triethylsilane at 30 degreesC, and 1,4-bis(trimethylsilyl)butadiyne with triethylsilane to yield (E)-2-triethylsilyl-1,4-bis(trimethylsilyl)-1-buten-3-yne at 60 degreesC was investigated. Pt(PPh3)(2)(PhC2Ph) was the best catalyst for these reactions. Compound 5 is completely inactive. A combination of evidence suggests that the catalytic activity exhibited by the mixed-metal cluster complexes is produced principally by fragmentation products which are almost certainly mononuclear platinum complexes. (C) 2000 Elsevier Science B.V. All rights reserved.