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

Reaction of CpRu(cod) Cl with phenylacetylene and AcOH gives an unusual binuclear ruthenium complex CpRu(mu-sigma, eta(3): eta(3), sigma-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-diphenyl3a, 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-1acetoxy- 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. (C) 2013 Elsevier B.V. All rights reserved.