he water-soluble complex Ru(H)(2)(CO)(TPPMS)(3) where TPPMS: (C6H5)(2)P(m-C6H4SO3Na) was obtained by phosphine ligand exchange from the corresponding PPh3 derivative in a water-toluene mixture and characterized by FTIR, UV-Vis, and H-1 NMR and P-31 {H-1} spectroscopy. The complex was used as a catalyst precursor for the aqueous-biphasic catalytic hydroformylation of several alkenes and alkene mixtures under moderate reaction conditions. The activity trend observed was: 1-hexene > cyclohexene > 2,3-dimethyl-1-butene and the catalyst was shown to be resistant to possible Sulphur poisons. (C) 2003 Elsevier B.V. All rights reserved.