Electrochemical study of the role of a H-bridged, unsymmetrically disubstituted diiron complex in proton reduction catalysis

The electrochemical behaviour of the unsymmetrically disubstituted [Fe2(CO)4(κ2-dppe)(μ-pdt)(μ-H)]+ (1μH+) complex was studied by cyclic voltammetry (CV) in MeCN– and CH2Cl2–[NBu4][PF6] both in the absence and in the presence of acid (HBF4 · Et2O or HOTs). In the absence of acid, 1μH+ undergoes a reversible one-electron oxidation and two-successive one-electron reductions, the first of which is partially reversible. In contrast to symmetrical analogues, 1μH+ does not regenerate its neutral precursor 1 upon reduction on the CV timescale. When acid is present, the reduction leads to catalytic proton reduction at a mild potential (ca. −1.3 V vs. Fc+/Fc) according to an original mechanism where 1μH+ is the catalyst. A second proton reduction process at −1.5 V is also observed for both HBF4 · Et2O and HOTs. The latter is proposed to be catalysed by the one-electron reduced form of the H-bridged complex, 1μH.