Reactions of molybdenocene and tungstenocene derivatives [M(Cp)2(H)2], [M(Cp)2H(OTs)], or [M(Cp)2H(μ-Li)}4] (M = Mo, W) with [Co2(CO)8] or [Co(CO)4]− gave [M(Cp)2H(CO)]+[Co(CO)4]− and [M(Cp)2(μ-H)(μ-CO)Co(CO)3] depending on the reaction conditions employed. These ionic heterobimetallic complexes were characterized by IR and NMR, as well as by X-ray diffraction analyses. A possible mechanism for the