Arsine, Stibine and Phosphine Derivatives of [Fe₂(CO)₆(μ-bdt)] (bdt = Benzenedithiolate): Syntheses, Structures and Spectroscopic and Electrocatalytic Studies

The reactivity of the benzenedithiolate (bdt)-bridged complex [Fe₂(CO)₆(µ-bdt)] with arsine, stibine and phosphine ligands has been studied. The new mono- and disubstituted complexes [Fe₂(CO)₅(EPh₃)(µ-bdt)] (E = As, 1; E = Sb 3) and [Fe₂(CO)₄(EPh₃)₂(µ-bdt)] (E = As, 2; E = Sb, 4) and the previously reported [Fe₂(CO)₄(PPh₂H)₂(µ-bdt)] (5) have been prepared by Me₃NO-initiated carbonyl substitution reactions of [Fe₂(CO)₆(µ-bdt)] with appropriate ligands at 80 °C. Spectroscopic and single-crystal X-ray diffraction studies reveal that in all cases the introduced ligands occupy apical coordination site(s) lying trans to the iron–iron bond. Their electrochemistry has been probed by cyclic voltammetry and selected complexes have been tested as proton reduction catalysts. Monosubstituted complexes 1 and 3 show two irreversible reductions at ca. −1.7 V and −2.0 V, respectively, relative to Fc⁺/Fc, while the disubstituted complexes 2 and 5 show a single irreversible reduction at ca. −2.2 V and −1.84 V, respectively. Complexes 1, 3 and 5 can catalyse electrocatalytic proton reduction in the presence of either p-toluene sulfonic acid (TsOH) or trifluoroacetic acid (CF₃CO₂H).