Treatment of [Mo2(Cp)2(μ-SMe)3(MeCN) 2]+ (1+) with NO3- or NO2- results in the conversion of one terminally bound acetonitrile ligand into an amidato bridge. The reaction produces [Mo 2(Cp)2(μ-SMe)3μ-η1, η1-OC(Me)NH]0/+ (20/+) and involves the formation of an intermediate, which was detected by cyclic voltammetry but which could not be isolated, and which likely arises from the substitution of the NOx anion for one MeCN ligand. The electrochemical behaviour of 2+ was studied by cyclic voltammetry in THF and MeCN. The reduction of 2+ in the presence of acid (HBF4/H2O or HBF4/ Et2O) in these solvents leads to the release of the amidate bridge. Controlled-potential electrolysis of 2+ in MeCN in the presence of acid produces 1+ quantitatively; the charge consumed (>1 F mol-1 of 1+) indicates that electrons are also used to reduce protons. This was confirmed by the formation of 2+ (in variable amounts depending on the conditions) on treating 2 with acid. © Wiley-VCH Verlag GmbH & Co. KGaA, 2005.