Insertion of tin(II) halides into [Co(CO)3L]2 compounds gives [trans-(CO)3LCo]2SnX2[X = Cl, Br, I; L = CO, Ph3P, Bun3P, or (PhO)3P], which were converted into the corresponding diethyl-, diphenyl-, or monophenylchloro-derivatives by Grignard reagents. The infrared spectra and a possible mechanism are discussed.