The thiolato-bridged binuclear molybdenum complexes [Mo2CP2L2(mu-SMe)(2)(mu-L’)]Y (Cp = eta(5)-C5H5; L’ = SMe, L = Bu’NC (1a), xylNC (1b) or CO (3); L’ = PPh2, L = Bu’NC (16); Y = BF4, Cl) react with the anionic reagents NaBH4, NaBD4, LiR (R = Me, Bu-n), R’MgCl (R’ = Me, Pr-i, Bu-n or Ph). The products are unsubstituted (5, 7) or substituted (8-12) eta(4)-cyclopentadiene derivatives, [Mo-2(eta(5)-C5H5,)(eta(4)-C5H5R)L-2(mu-SMe)(3)] (L = xylNC, CO), or mu-formimidoyl dinuclear products, [Mo2CP2L2(mu-SMe)(2)(mu-L’)(mu-CHNR)] (L’ = SMe, L = (BuNC)-N-t (4) or xylNC (6); L’ = PPh2, L = (BuNC)-N-t (17)). Since the reduced dinuclear species [Mo2CP2(CO)(2)(mu-SMe)(2)] and the related oxo-compound [Mo2CP2(CO)(O)(mu-SMe)(2)] are sometimes isolated as minor products, the anionic reagent can play a secondary role as a reductant in these reactions in addition to its main role as a nucleophile. The electronic properties of the donor carbon atoms of the cyclopentadienyl rings and of the terminal ligands L, together with the nature of the anionic reagent, are the dominant factors controlling selective formation of 4-12 and 17. Tetrafluoroboric acid reacts with the substituted cyclopentadiene derivatives 9, 11 and 12 to form new functionalised cyclopentadienyl derivatives, [Mo-2(eta(5)-C5H5)(eta(5)-C5H4R)(CO)(2)(mu-SMe3](BF4) (R = Me (13), Bu-n (14) or Ph (15)). New complexes have been characterised by spectroscopic and chemical methods, supplemented for 5, 6 and 12 by X-ray diffraction studies at 100 K. (c) 2005 Elsevier B.V. All rights reserved.