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

The synthesis of phosphineimidazolyl 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.