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)Cl(2)}(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.