A Cyclometalated Ruthenium-NHC Precatalyst for the Asymmetric Hydrogenation of (Hetero)arenes and Its Activation Pathway

This study describes the structural investigation of a highly versatile ruthenium-NHC (N-heterocyclic carbene) catalyst complex, which has been established for the asymmetric hydrogenation of various aromatic compounds. A complex containing an unusual doubly deprotonated NHC ligand was isolated and identified as the precatalyst to this complex. When its subsequent reactivity was monitored, two additional precatalysts, featuring partially hydrogenated naphthyl substituents, were characterized spectroscopically. Ligand hydrogenation appears to be a key activation process en route to the active catalyst.