Ruthenium complexes mixed donor ligands

Ruthenium(ii).—Group VII Donors. Halide donor ligands. A study has shown that the blue complexes obtained by electrolytic reduction of H2[RuCl5H20] in acidic solution are further examples of mixed Ru"-Ru " complexes. They were previously assumed to contain only Ru . Dimers of the type Ru2Ch3Vi," (n = 0,1, or 2) were separated and isolated using ion-exchange chromatography. 

On the other hand, the ruthenium complex of ferrocenyl-alkynyl dimer shows a separation of redox potentials of two ferrocene units through the alkyne-Ru-alkyne ligand at 0.22 This result indicates that the mixed-valence state of ferrocenyl groups in Ru(-C=C Fc)2(dppm)2 complex are much more stable because of the strong donor-acceptor interaction through the ruthenimn core metal with two a-bonding alkynyl chains. The four oxidation states could be experimentally foimd for Ru(H =C Fc)2(dppm)2 complex (Fe(II)-Ru(II) Fe(II) Fe(III) Ru(II) Fe(II) Fe(III) Ru(II)-Fe(in) Fe(III)-Ru(III)-Fe(III)), where the redox potential of the ruthenium center is positively shifted as noted above. 

There have been only a handful of studies on exchange coupled ruthenium dimers and yet the information available on metal-metal coupling is potentially as valuable as that obtained from mixed-valence complexes. The reason for this lack of activity has been the greater familiarity of researchers with the chemistry of Ru(II) bound to 7r-acid ligands. The synthetic pathways to complexes of this type are well explored (7) and possess the tremendous advantages of stability and ease of handling. Ru(II) complexes that incorporate anionic n donor... 

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