In a water/chlorobenzene biphasic reaction, the hydrogenation of trans-cinnamaldehyde, catalyzed by water-soluble Ru(II)-phosphane complexes at pH 3.04 (phosphate buffer), produces a 61:39 mixture of cinnamyl alcohol and dihydrocinnamaldehyde at 1 bar H-2; however, the selectivity is increased to 93:7 by increasing the hydrogen pressure to 8 bar.