Phosphine-Imidazolyl Ligands for the Efficient Ruthenium-Catalyzed Hydrogenation of Carboxylic Esters

The synthesis of phosphine–imidazolyl ligands 1 and 2 in good yields is presented. In combination with [{Ru(benzene)Cl2}2], ligands 1 c and 1 e formed efficient catalyst systems for the selective hydrogenation of various carboxylic esters into their corresponding primary alcohols. Furthermore, the structures of four ruthenium complexes with ligands 1 b, 1 c, 1 d, and 1 e were determined by X‐ray crystallography, which showed the formation of different coordination modes depending on the ligand structure. P‐N the tail on the donkey: The combination of [{Ru(benzene)Cl2}2] and P‐N ligand 1 e was active in the hydrogenation of aromatic esters and lactones, whilst [{Ru(benzene)Cl2}2]/1 c attained good results in the reduction of aliphatic lactones and esters (see scheme).