An Anionic Dinuclear Ruthenium Dihydrogen Complex of Relevance for Alkyne gem-Hydrogenation

During an investigation into the fate of ruthenium precatalysts used for light-driven alkyne gem-hydrogenation reactions with formation of Grubbs-type ruthenium catalysts, it was found that the reaction of [(IPr)(eta(6)-cymene)RuCl2] with H-2 under UV-irradiation affords an anionic dinuclear sigma-dihydrogen complex, which is thermally surprisingly robust. Not only are anionic sigma-complexes in general exceedingly rare, but the newly formed species seems to be the first example lacking any structural attributes able to counterbalance the negative charge and, in so doing, prevent oxidative insertion of the metal centers into the ligated H-2 from occurring.