Reversibility of Disubstituted Vinylidene−Internal Alkyne Isomerization at Cationic Ruthenium and Iron Complexes

The cationic disubstituted vinylideneruthenium complexes [CpRu{CC(Ph)R}(dppe)][BArF4], which are prepared directly from internal alkynes via 1,2-migration of carbon substituents, are shown to undergo disubstituted vinylidene-to-internal alkyne isomerization on reaction with a monophosphine. The observation provides the first examples in which the reversible conversion between internal alkynes and disubstituted vinylidenes is experimentally confirmed, and the kinetic and mechnistic investigations indicated that an uncommon electrophilic 1,2-migration of the carbon substituents takes place in the internal alkyne−disubstituted vinylidene interconversion.