Reactivity of 1,3-ynone in transformation of Ru2–Ru4 clusters: Formation of ruthenoles via tetraruthenium intermediate

A robust “soft and hard” alkyne ligand, 1,3-ynone, induced the stepwise transformation of ruthenium carbonyl clusters. The thermolysis reactions of Ru3(CO)12 (1) with 1-(4-methoxyphenyl)-3-phenylprop-2-yn-1-one (2) were systematically investigated. A diverse range of products formed via finely tuning the molar ratios of the reactants. When 1 reacted with one equivalent of 2, triruthenium cluster 3 and tetraruthenium cluster 4 were isolated. Further increasing 2 led to the formation of three ruthenoles 5a, 5b and 5c, in which the ynone moieties couple in head to head, head to tail and tail to tail modes, respectively. The cluster compounds 3, 4 and 5a–b were fully characterized and their molecular structures were determined by single crystal X-ray diffraction. The crystal structures clearly demonstrated the activation of the alkyne ligand and the transformation of cluster skeletons. The fluxionality of the alkyne coordination was observed in the crystal structure of 3. It is on the tetraruthenium framework of 4 that the coordinated C–C triple bond is activated. To elucidate the formation pathway of the ruthenoles, the reaction of 2 and 1,3-ynone capped cluster 3 was investigated. The experimental results confirmed that 4 is the intermediate for three ruthenoles, which sheds light on the alkyne mediated fragmentation and formation of low-valence ruthenium carbonyl clusters.