The complexes π-C5H5(CO)3M·GeR3(M = Mo, W; R = Me, Et, Prn) are stable to water, but are oxidised in air. They are thermally stable to 200° and sublime readily in vacuo Infrared, proton magnetic resonance, and mass spectra are reported. Diethylphosphine displaces one CO group while reaction with Ph3P gives evidence of an intermediate, π-C5H5(CO)3(Ph3P)M,GeR3, which decomposes to π-C5H5(CO)2(Ph3P)·MGeR3. Reagents which cleave the metal–germanium bond are: HCl, C2H4Br2, EtBr, and l2. The latter, present in excess, also displaces CO giving π-C5H5(CO)2Ml3. Magnesium bromide also cleaves the M–Ge bond forming the transition metal-Grignard reagents which probably involve 3-co-ordinate magnesium, π-C5H5(CO)3M·MgBr(THF). Mercuric chloride also cleaves the W–Ge bond giving π-C5H5(CO)3W·HgCl which, in preliminary studies, has been further used in the cleavage of other metal–metal bonds.