Reactions of the cyclopentadienyl ruthenium complexes (C5R5)Ru(cod)Cl and [(C5R5)Ru(MeCN)3]+ (R = H, Me) with phenylacetylene and acetic acid: Unexpected difference in reactivity of CpRu and Cp*Ru complexes

•Difference in reactivity of CpRu and Cp*Ru complexes was revealed.•Unusual binuclear ruthenium complex with bridging flyover ligand was obtained.•Rare example of reaction between Cp ligand and alkyne was found.

Reaction of CpRu(cod)Cl with phenylacetylene and AcOH gives an unusual binuclear ruthenium complex CpRu(μ-σ,η3:η3,σ-C6H3Ph3)RuCp (5, 58% yield) with a bridging acyclic flyover ligand C6H3Ph3. Under similar conditions [CpRu(MeCN)3]+ undergoes an unexpected cleavage of Cp ligand giving 4,7-diphenyl-3a,7a-dihydroindene (6, 65% yield). In sharp contrast, the pentamethylated congeners Cp*Ru(cod)Cl and [Cp*Ru(MeCN)3]+ react with phenylacetylene and AcOH in catalytic fashion giving 1,4-diphenyl-1-acetoxy-1,3-butadiene. The structures of 5 and 6 were established by X-ray diffraction. The mechanism of Cp ligand cleavage was proposed on the basis of DFT calculations.

Graphical abstractA striking difference between reactions of CpRu and Cp*Ru complexes with alkynes was revealed. While Cp*Ru(cod)Cl and [Cp*Ru(MeCN)3]+ catalyze coupling of phenylacetylene with addition of acetic acid, the CpRu congeners are converted into unusual flyover complex or undergo cleavage of Cp ligand.Figure optionsDownload full-size imageDownload as PowerPoint slide