The new water soluble complex RuH(CO)(NCMe)(TPPMS)(3)[BF4] has been synthesized by the interaction of RuHCl(CO)(TPPMS)(3) with one equivalent of NaBF4 in acetonitrile. The complex was characterized by spectroscopic techniques, and it shows high stability in water demonstrated by UV-Vis measurements. Because of this property, it can be used as a catalyst precursor for the liquid-liquid biphasic hydrogenation of various alkenes, such as 1-hexene, 1-decene, allylbenzene, styrene, cyclohexene, and 1-methyl cyclohexene. The catalytic activity of this complex is highly dependent of the reaction conditions as well as the type of substrate employed. Under normal conditions, the reaction order will be 1-hexene > cyclohexene > allylbenzene > 1-decene > styrene much greater than> 1-methyl-cyclohexane. This complex, can be recycled several times maintaining the same activity, the ruthenium remains in the aqueous phase without indication of partition of the complex between the water and the organic phase. (C) 2003 Elsevier B.V. All rights reserved.