AbstractThe displacement of terminal CO ligands in Fe2(μ‐Se2C3H5CH3)(CO)6 (1) by triphenylphosphane, trimethyl phosphite, and bis(diphenylphosphanyl)ethane (dppe) ligands is investigated. Treatment of 1 with 1 equiv. of triphenylphosphane afforded Fe2(μ‐Se2C3H5CH3)(CO)5(PPh3) (2). The mono‐ and disubstituted phosphite complexes Fe2(μ‐Se2C3H5CH3)(CO)5P(OMe)3 (3) and Fe2(μ‐Se2C3H5CH3)(CO)4[P(OMe)3]2 (4) were obtained from the reaction of 1 with excess P(OMe)3 at reflux in toluene. In contrast, the reaction of 1 with 1 equiv. of dppe in the presence of Me3NO·2H2O gave a mixture of Fe2(μ‐Se2C3H5CH3)(CO)4(κ2‐dppe) (5) and [Fe2(μ‐Se2C3H5CH3)(CO)5]2(μ‐dppe) (6). The newly synthesized complexes 2–6 were fully characterized by IR, 1H NMR, 13C NMR, 77Se{1H} NMR, and 31P{1H} NMR spectroscopy, mass spectrometry, elemental analysis, and X‐ray diffraction analysis. Complex 2 has proved to be a catalyst for the electrochemical reduction of the weak acid, acetic acid, to give molecular hydrogen. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)