Reactions of metal carbonyl anions, CpFe(CO)2−, Re(CO)5−, Mn(CO)5−, CpMo(CO)3−, CpCr(CO)3−, and Co(CO)4−, with CrCl3•3S (S = THF, CH3CN) and reactions of Mn(CO)5− and Re(CO)5− with [Co(o-phen) 2Cl2]ClO4 are reported. Net oxidation/reduction chemistry is observed with formation of metal carbonyl dimers and CrCl2•4S or Co(o-phen)2Cl2. Metal carbonyl halides are also observed and shown to arise from a secondary reaction of the metal carbonyl dimer with the oxidant. The products and rates are most consistent with outer-sphere electron-transfer reactions. Reactions of CpFe(CO)2− with CpFe(CO)2X (X = Cl, Br, I) are also reported. The rate dependence on X is very small and in the order expected for nucleophilic substitution.