Dimolybdenum thiolate-bridged complexes [Mo2Cp2(mu-SMe)(2)(mu-SCH2CH2E)] (E = O (2) or NH (4)) with a proton-dependent protecting device have been synthesized by reaction of [Mo2Cp2(mu-SMe)(2)(mu-Cl)2] (1) with SCH2CH2EH. The reactivity of the resultant quadruply bridged complexes with acid was investigated in the absence and in the presence of a potential ligand (N-2, MeCN, RNC). While the protonation of complexes 2 and 4 under N-2 in dichloromethane produced only the oxidized derivatives instead of the desired diazenido compound, ligand binding was observed in MeCN or in the presence of RNC (R = t-Bu, Xyl). Whereas acetonitrile loss from [Mo2Cp2(mu-SMe)(2)(mu-SCH2CH2OH)(MeCN)(2)](+) (8(+)) prevented the isolation and characterization of this species, the t-BuNC analogue (6(+)) could be characterized by an X-ray crystal structure. The electrochemistry of 2 and 2(+) was investigated in CH2Cl2 and in MeCN, both in the absence and in the presence of acid. While the addition of HBF4 center dot Et2O to a dichloromethane solution of 2 only produced 2(+) (and presumably H-2), 8(+) was the major product of the protonation in MeCN.