Highly Active Catalysts in Alkene Metathesis: First Observed Transformation of Allenylidene into Indenylidene via Alkenylcarbyne—Ruthenium Species

A cat. for all seasons: The transformation of the allenylidene-ruthenium complexes [RuCl(η6-arene)(CCCR2)(PR)][CF3SO3] into indenylidene species [RuCl(η6-arene)(indenylidene)(PR)][CF3SO3]2 by the simple protonation with CF3SO3H and formation of an alkenylcarbyne intermediate (see picture; arene=p-cymene) is observed by low temperature NMR experiments. The new in situ generated 18 electron ionic indenylidene species are highly active in the polymerization of cyclooctene and cyclopentene, ring-closing metathesis of dienes and enynes, and the acyclic diene metathesis of decadiene, thus making it a catalyst for all seasons.