The importance of cluster fragmentation in the catalytic hydrogenation of phenylacetylene by PtRu5 carbonyl cluster complexes

PtRu5(CO)13(PBu3t)(μ3-PhC2H)(μ5-C)(2) has been shown to be a catalyst precursor for the hydrogenation of PhC2H to styrene and ethylbenzene. Three new organometallic products have been found in the catalyst solutions. These are Ru5(CO)12(μ5-C)[PtPBu3t](μ3-PhC2H)(μ-H)2(4), Pt(PBu3t)(PhC2H)(CO)(5), and Ru5(CO)11(μ4-CCHCPh)(μ4-HC2Ph)(μ3-HC2Ph) (6). Compounds 4–6 have been synthesized independently and structurally characterized and each one has been tested independently for its ability to produce hydrogenation of PhC2H catalytically. Compound 4 contains an open square-pyramidal cluster of five ruthenium atoms with one platinum atom bridging an edge of the cluster. It is structurally related to 2 but contains one less CO ligand and two hydrido ligands formed by the addition of one equivalent of hydrogen to the metal cluster. It can be obtained directly from 2 by reaction with hydrogen in the presence of trimethylamine oxide. Compound 5 is a tricoordinated mononuclear platinum complex containing one PBu3t ligand, one CO ligand and one μ2-PhC2H ligand. Compound 5 can be obtained directly from Pt(PBu3t)2 by reaction with PhC2H under an atmosphere of CO. Compound 6 was obtained from the reaction of Ru5(CO)15(μ5-C) with PhC2H in the presence of UV–Vis irradiation. Compound 6 contains three equivalents of PhC2H; one is present as triply bridging PhC2H ligand; one is a quadruply bridging ligand; the third one has formed a bond to the carbido ligand in the center of the metal cluster to form a novel tetra-metallated allyl ligand. Compound 5 has the highest catalytic activity of all three compounds and is believed to be responsible for the vast majority of the catalytic hydrogenation produced from the solutions of 2. Compound 4 is transformed into 5 under the conditions of catalysis.

Graphical abstractPtRu5(CO)13(PBu3t)(μ3-PhC2H)(μ5-C)(2) has been shown to be a catalyst precursor for the hydrogenation of PhC2H to styrene and ethylbenzene. Three new organometallic products have been found in the catalyst solutions. These are Ru5(CO)12(μ5-C)[PtPBu3t](μ3-PhC2H)(μ-H)2(4), Pt(PBu3t)(PhC2H)(CO)(5) and Ru5(CO)11(μ4-CCHCPh)(μ4-HC2Ph)(μ3-PhC2H) (6). Compounds 4–6 have been synthesized independently and structurally characterized and each compound has been tested independently for its ability to produce hydrogenation of PhC2H catalytically. Compound 5 is significantly more active than 4 or 6.Figure optionsDownload full-size imageDownload as PowerPoint slide