Thallium(I) tris(pyrazol-1-yl)methanesulfonate (TlTpms) has been prepared as a new versatile precursor for Tpms complexes. TlTpms readily reacts with the rhodium(I) complexes [Rh(LL)Cl] 2 [LL = (CO) 2 , cod, nbd] to give the corresponding TpmsRh(LL) complexes [LL = (CO) 2 (2a), cod (3), and nbd (4)]. In solution, 2a reversibly forms the binuclear complex TpmsRh(µ-CO) 3 RhTpms (2b). 3 and 4 react with CO to form 2a. TpmsRh(CO)(PR 3 ) complexes [PR 3 = PPh 3 (5a), PMe 3 (5b), PCy 3 (5d), P(Ph) 2 (PhSO 3 K) (5e)] have been obtained by reaction of 2a with the corresponding phosphanes. The solidstate structures of 2a, 3, 4, and 5a have been determined by X-ray analysis. 2a, 3, and 5a have square-planar geometries