Facile Migratory Insertion of a N-Heterocyclic Carbene into a Ruthenium−Carbon Double Bond: A New Type of Reaction of a NHC Ligand

The reaction of [RuCp(IPri)(CH3CN)2]PF6 (IPri = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with HC⋮CR (R = COOMe, COOEt, COMe) yields the allyl carbene complexes [RuCp(C(R)-η3-CHC(R)CH−IPri)]PF6. This conversion involves selective head-to-tail coupling of two alkynes and an unusual migratory insertion of the N-heterocyclic carbene into the ruthenium−carbon double bond of a ruthenacyclopentatriene intermediate.