The Cp2Fe+ oxidation and the protonation of CpMoH(CO)2L (L: PPh3, 1; PMe3, 2) in MeCN have been investigated. In the dry solvent, the oxidation of both compounds consumes 1 mol of oxidant/mol of hydride with production of [CpMo(CO)2L(MeCN)]+ (L: PPh3, [3]+; PMe3, [4]+) and H2. The stoichiometry changes toward the consumption of 2 mol of oxidant in the presence of excess water when the oxidizing equivalents are added rapidly, either chemically or electrochemically. However, 1 oxidizing equiv is again sufficient to consume the hydride material completely under conditions of slow oxidation. Under comparable conditions, the more basic 2 leads to a lower [ox]/M−H stoichiometry. Protonation of 1 and 2 with HBF4·Et2O in dry MeCN results in rapid H2 evolution and formation of [3]+ and [4]+, respectively, whereas the presence of excess water suppresses the H2 evolution and gives rise to protonated water. However, this process is followed by slow and irreversible delivery of the proton back to 1 or 2 to afford [C...