The main advances, over the last two decades, on dinuclear complexes featuring a redox-active ligand close to the bimetallic core are presented in this chapter. At the end of the nineties, the discovery of the structure of the active site of [FeFe]-hydrogenases has led to a revival of the chemistry of dithiolato/bis-thiolato bridged carbonyl di-iron complexes with the aim of understanding the functioning, at the molecular level, of this family of metallo-enzymes and to reproduce their activity towards the reversible H+/H2 conversion. The progress in the knowledge of the H-cluster reveals that its high activity is due to an efficient and subtle Nature’s engineering that involves a dinuclear activating framework and its cooperativity with redox-active ligand and proton-relay. If initially the development of this chemistry has been centred on the preparation of rudimentary di-iron compounds in order to study their ability to reduce protons electrochemically or photochemically, more sophisticated systems with a relay of protons, for promoting proton transfers, have rapidly emerged. Paradoxically, it is only quite recently that an increasing number of derivatives incorporating a redox-active ligand has been elaborated. To date, there are only a few di-iron compounds capable of reproducing H-cluster activity. These researches are still ongoing and they have contributed to develop the chemistry of dinuclear complexes with redox ligands.
The first part of this chapter is dedicated to the advances in this di-iron bio-inspired chemistry, which has led to consider the combination of carbonyl di-iron platforms with a large series of redox ligands and the different ways for introducing them near the di-iron core. Examples of hetero-bimetallic [NiFe] species featuring a redox group, considered as models of the [NiFe]-hydrogenases, are also presented.
Considering the renewal of the interest in using bimetallic systems for molecular activation in order to develop novel catalytic processes, the second part of this chapter presents selected examples of bimetallic derivatives featuring chelating redox-active ligands. Their properties/activities, often original or unexpected, in connection with the presence of the redox-active ligand in the coordination sphere of a dinuclear framework, are described. These results, even if their presentation in this chapter may appear somewhat scattered, demonstrate that the combination of “non-innocent” ligands (redox-active in this chapter but also proton-responsive) with dinuclear sites offers interesting perspectives in the field of molecular activation with transition metal complexes.
