Ruthenium, dinuclear complexes, redox

Bielawski et al. have developed Janus-head dicarbene ligands which are able to act as a bridge between two metal centers, thereby leading to dinuclear complexes of type 96 [58-60] (Fig. 32). More recently homonuclear bimetallic ruthenium(II) and iron(II) complexes 97 have been synthesized. It was hoped that the dicarbene ligand would interconnect the redox-active metal centers, but the... 

Ruthemum(iii).—Ruthenium(iii) complexes [RuX(NH3)s] +, where X = halide or azide, react even in the dark by parallel aquation and redox paths. The latter at least must involve intramolecular electron transfer. For X = chloride, the direct aquation path predominates, but for X = azide, the redox path is more significant, yielding molecular nitrogen complexes of ruthenium(ii). The rate constant for aquation of the dinuclear molecular nitrogen complex [(H3N)5RuN2Ru(NH3)s] + has been determined at 25-0... 

We have now constructed the missing ligands needed to prepare the other possible isomers of the dinuclear cyclometallates (Figure 25). Each of these compounds forms bis-metallated complexes [(tpy)Ru(L)Ru(tpy)]2+ which are generally similar to the isomeric compounds with CNs donor sets at each end. However, they exhibit a single ruthenium(n)/(ni) redox process at +0.15 V. 

Very recently a new kind of electrocatalyst has been propounded using the dinuclear quinone-containing complex of ruthenium (25).492,493 Controlled-potential electrolysis of the complex at 1.70 V vs. Ag AgCl in H20 + CF3CH2OH evolves dioxygen with a current efficiency of 91% (21 turnovers). The turnover number of 02 evolution increases up to 33,500 when the electrolysis is carried out in water (pH 4.0) with an indium-tin oxide(ITO) electrode to which the complex is bound. It has been suggested that the four-electron oxidation of water is achieved by redox reactions of not only the two Run/Ruin couples, but also the two semiquinone/quinone couples of the molecule. 

Comparison of Redox Potentials and Comproportionation Constants for Symmetrically Substituted Dinuclear Osmium and Ruthenium Complexes... 

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