Complexes of the type [M(CO)(SnCl3)2Cl]–(M = Pd, Pt) have been synthesized by substitution of carbon monoxide into palladium–trichlorotin and platinum–trichlorotin compounds. The in situ reactivity of solutions containing the carbonyl–metal–tin complexes of both metals is described and compared. I.r. spectra (1800–2200 and 60–400 cm–1 regions), visible–u.v. spectra and conductivity data of the complexes are discussed.