Abstract Addition of 1 equiv. of a phosphane or phosphite ligand to the κ 3-bonded [Tp Me2 Rh (CO) 2] and [Tp Me2, 4Cl Rh (CO) 2] dicarbonyl precursors gives the monosubstituted complexes [TpRh (CO) L]. The X-ray crystal structures show that the three complexes [Tp Me2 Rh (CO)(PMe 3)],[Tp Me2 Rh (CO)(PMePh 2)], and [Tp Me2, 4Cl Rh (CO)(PMePh 2)] adopt square-planar geometries. The X-ray crystal structure of [Tp Me2 Rh (CO){P (OPh) 3 ...