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

The electrochemical behaviour of the unsymmetrically disubstituted [Fe 2 (CO) 4 (κ 2 -dppe)(μ-pdt)(μ-H)] + ( 1μH + ) complex was studied by cyclic voltammetry (CV) in MeCN– and CH 2 Cl 2 –[NBu 4 ][PF 6 ] both in the absence and in the presence of acid (HBF 4 · Et 2 O 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 HBF 4 · Et 2 O and HOTs. The latter is proposed to be catalysed by the one-electron reduced form of the H-bridged complex, 1μH .