Triruthenium–iridium clusters containing alkyne ligands: synthesis, structure, and catalytic implications of [(μ-H)IrRu3(CO)11(μ3-η2-PhCCPh)] and [IrRu3(CO)10(μ4-η2-PhCCPh)(μ-η2-PhCCHPh)

Abstract

The mixed-metal cluster [HIrRu3(CO)13] 1 reacts with one equivalent of disubstituted alkynes RCCR to give [HIrRu3(CO)11(µ3-η2-RCCR)] (R = Ph 2; R = Me 3), with a second equivalent of the alkyne the clusters [IrRu3(CO)10(µ4-η2-RCCR)(µ-η2-RCCHR)] (R = Ph 4; R = Me 5) are obtained. The single-crystal X-ray structure analyses of 2 and 3 show these clusters to have a tetrahedral Ru3Ir framework containing the alkyne ligand coordinated in a parallel fashion over the Ru3 face of the metal skeleton. In contrast, the clusters 4 and 5 consist of a butterfly arrangement of the Ru3Ir framework with the alkyne ligand coordinated to all four metal atoms, giving an overall octahedral Ru3IrC2 skeleton, as demonstrated by the single-crystal structure analysis of 4. Cluster 1 is an excellent catalyst for the hydrogenation of diphenylacetylene to give stilbene (catalytic turnover number 990 within 15 min), clusters 2 and 4 are also catalytically active but seem to represent side-channels of the catalytic cycle.