The synthesis and characterization of a series of water-soluble cobalt carbonyl complexes is described: HCo(CO) 3 (TPPTS), HCo(CO) 2 (TPPTS) 2 , and [Co(CO) 3 (TPPTS)] - , where TPPTS=P(m-C 6 H 4 SO 3 Na) 3 . Investigation of the substitution of Co 2 (CO) 5 by TPPTS shows that the reaction process via the ionic intermediate [Co(CO) 3 (TPPTS) 2 ] [Co(CO) 4 ], which is relatively stable in water