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Abstract

The light-driven gem-hydrogenation of internal alkynes in the presence of [(NHC)(η⁶-cymene)RuCl₂] generates discrete ruthenium carbene complexes. When applied to appropriately designed enyne substrates, the reactive intermediates thus formed will engage the tethered olefin in metathetic ring closure while splitting off a Hoveyda–Grubbs-type complex as secondary carbene. This unconventional approach to these classical catalysts for olefin metathesis rivals existing methodology in that it is safe, short, phosphine-free, and uses readily available starting materials.