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)(kappa(2)-dppe)(mu-pdt)(mu-H)](+) (1 mu H+) complex was studied by cyclic voltammetry (CV) in MeCN- and CH2Cl2-[NBu4][PF6] both in the absence and in the presence of acid (HBF4 center dot Et2O or HOTs). In the absence of acid, 1 mu H+ undergoes a reversible one-electron oxidation and two-successive one-electron reductions, the first of which is partially reversible. In contrast to symmetrical analogues, 1 mu H+ 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 1 mu H+ is the catalyst. A second proton reduction process at 1.5 V is also observed for both HBF4 center dot Et2O and HOTs. The latter is proposed to be catalysed by the one-electron reduced form of the H-bridged complex, 1 mu H. (C) 2008 Elsevier B.V. All rights reserved.