Reactions of (CMe2)(SnMe2) doubly bridged biscyclopentadienes with transition metal carbonyls: Double ring-to-metal migration of SnMe2

In the reactions of doubly bridged biscyclopentadienes (C5H3R(CMe2))(C5H3R(SnMe2)) (R = H (1c), tBu (2)) with M(CO)n (M = Fe, n = 5; M = Mo, n = 6) in refluxing xylene, the bridging SnMe2 group migrates from the ligand to the corresponding transition metal atoms to give compounds (3, meso- and rac-5, meso- and rac-7) containing the M–Sn–M units; together with the corresponding destannylated products (4, meso- and rac-6, meso- and rac-8); the bridging group CMe2 does not migrate. A plausible pathway for migration of SnMe2 group is proposed. The photochemistry of complexes containing the M–Sn–M unit was also studied. The molecular structures of cis-2, rac-5, and meso-7 were determined by X-ray diffraction.