In the reactions of double-bridged biscyclopentadienes (EMe 2 )(SnMe 2 )(RC 5 H 3 ) 2 (E=C (1), E=Si (2 or 4), E=Ge (3)), or single-bridged biscyclopentadiene (SnMe 2 )( t BuC 5 H 4 ) 2 (5) with Mo(CO) 6 in refluxing xylene, the bridging SnMe 2 group migrates from the ligand to the molybdenum atoms to give compounds (6–10) containing the Mo–Sn–Mo units; the bridging group EMe 2 (E=C or Si in 1, 2, or 4) does not migrate. It is noteworthy that [(η 5 -C 5 H 5 )Mo(CO) 3 ] 2 SnMe 2 (8) obtained from the reaction of (GeMe 2 )(SnMe 2 )(C 5 H 4 ) 2 (3) with Mo(CO) 6 is a degermylated and SnMe 2 group migrated product, another outcome worth mentioning is that the complex 9 is afforded only in the rac-configuration. The stability of complexes (6, 7, and 10) containing the Mo–Sn–Mo unit toward heat and light was also studied. The molecular structures of 6, 9, and 10 were determined by X-ray diffraction.