The dianions {[ p-(CO) 3MC 5H 4C(O)] 2C 6H 4} 2− reacted with Ph 2SnBr 2 in a 1:2 or 1:1 ratio to give tetranuclear heterodimetallic complexes p-[(Ph 2BrSn)(CO) 3MC 5H 4C(O)] 2C 6H 4 (M=Mo ( 1) or W ( 2), respectively), and with CH 2(SnPhBr 2) 2 to yield tetranuclear heterodimetallic metallamacrocycles { p-[(CO) 3MC 5H 4C(O)] 2C 6H 4}{(Ph 2− n Br n Sn) 2CH 2} ( n=1, M=Mo ( 5) and W ( 6); n=0, M=Mo ( 7) and W ( 8), respectively). Only one bromide on the tin atom was replaced by the metallic anions owing to the electron-withdrawing groups on the cyclopentadienyl rings greatly decreasing the nucleophilicity of the metallic anions. Treatment of complexes 1 and 2 with Na 2S·9H 2O yielded the novel metallamacrocyclic complexes { p-[(CO) 3MC 5H 4C(O)] 2C 6H 4}{(Ph 2Sn) 2S} (M=Mo ( 3) and W ( 4), respectively). All compounds have been characterized by elemental analyses, IR and 1H-NMR spectra. The crystal structures of complexes 3 and 7 determined by X-ray crystallography indicate a novel 14-membered organometallic metallamacrocyclic ring system in which two Mo–Sn units are linked by the bridging cyclopentadienyl ligand and the sulfur or carbon atom. In addition, the carbonyl group π-system is coplanar with the adjacent cyclopentadienyl ring system, but markedly deviates from the bridging phenyl plane.