η 1 ‐Vinylidene Formation from Internal Alkynones by C–C Bond Migration

The [μ 2 ‐N 2 {CpRu(PPh 3 ) 2 } 2 ] 2+ ( 1 2+ ) dication is a source of the formal 16‐electron [CpRu(PPh 3 ) 2 ] + fragment, and it reacts with internal alkynes such as 1,3‐diphenylpropynone, 4‐phenyl‐3‐butyn‐2‐one, and 3‐cyclopropyl‐1‐phenylpropynone to yield η 1 ‐vinylidene complexes 2a + – 2c + by C–C bond activation. In the case of 1,3‐diphenylpropynone, the η 1 ‐ketone complex [CpRu(PPh 3 ) 2 {PhC(η 1 ‐O)C≡CPh}] + ( 3a + ) was isolated as its PF 6 – salt, and it is apparently an intermediate in the formation of the vinylidene complex. Complexes 2a + – 2c + were characterized as their BAr F 4 – [ArF = 3,5‐bis(trifluoromethyl)phenyl] salts by NMR and IR spectroscopic methods, ESI‐MS, and EA. The single crystal X‐ray diffraction structure of 2a BAr F 4 is presented. These reactions represent the first examples where an internal alkyne undergoes C–C bond migration to form an η 1 ‐vinylidene complex. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)