The synthesis and full characterization of the water-soluble complex [Rh(mu-Pz)(CO)(TPPMS)](2) (I), where TPPMS is (C6H5)(2)P(m-C6H4SO3Na) and Pz pyrazolate, is described. Complex I was obtained by ligand exchange procedures under inert atmosphere and characterized by FT-IR, H-1 NMR, H-1{P-31} NMR, P-31 NMR and FAB-MS techniques. These analyses confirmed that there are two pyrazolate bridging ligands in an exobidentate orientation, giving a C-2v symmetry to the complex. The molecular weight of I was confirmed by FAB-MS, indicating the molecular formula stated above. The complex was active in the catalytic hydroformylation of 1-hexene and styrene in a two-phase reaction medium. Heptanal was the main product obtained for 1-hexene, while 2-phenylpropanal and 3-phenylpropanal were obtained from styrene. At the end of the reaction, all the metal remained in the aqueous phase, indicating that no metallic leaching observed during the catalytic reaction. (C) 2003 Elsevier B.V. All rights reserved.