Grubbs Metathesis Enabled by a Light‐Driven gem‐Hydrogenation of Internal Alkynes

[(NHC)(cymene)RuCl2] (NHC=N‐heterocyclic carbene) complexes instigate a light‐driven gem‐hydrogenation of internal alkynes with concomitant formation of discrete Grubbs‐type ruthenium carbene species. This unorthodox reactivity mode is harnessed in the form of a “hydrogenative metathesis” reaction, which converts an enyne substrate into a cyclic alkene. The intervention of ruthenium carbenes formed in the actual gem‐hydrogenation step was proven by the isolation and crystallographic characterization of a rather unusual representative of this series carrying an unconfined alkyl group on a disubstituted carbene center. The hydrogenation of enynes with [(NHC)(cymene)RuCl2] (NHC=N‐heterocyclic carbene) complexes under UV irradiation leads to the formation of cyclic alkenes through the intervention of Grubbs‐type ruthenium complexes. This unorthodox entry into the realm of metathesis chemistry represents the first light‐driven catalyst system that is able to instigate alkyne gem‐hydrogenation with concomitant formation of a discrete metal carbene species.